Nie wiedząc, jakiej wtyczki Google OAuth używasz (i w jaki sposób wewnętrznie loguje użytkownika), jedynym sposobem jest zastąpienie funkcji wtyczki wp_set_auth_cookieustawienie $remember zawsze true:

if ( ! function_exists( 'wp_set_auth_cookie' ) ) :
    /**
     * Sets the authentication cookies based on user ID.
     *
     * The $remember parameter increases the time that the cookie will be kept. The
     * default the cookie is kept without remembering is two days. When $remember is
     * set, the cookies will be kept for 14 days or two weeks.
     *
     * @since 2.5.0
     * @since 4.3.0 Added the `$token` parameter.
     *
     * @param int         $user_id  User ID.
     * @param bool        $remember Whether to remember the user.
     * @param bool|string $secure   Whether the auth cookie should only be sent over HTTPS. Default is an empty
     *                              string which means the value of `is_ssl()` will be used.
     * @param string      $token    Optional. User's session token to use for this cookie.
     */
    function wp_set_auth_cookie( $user_id, $remember = false, $secure="", $token = '' ) {

        /**
         * Force $remember 
         */
        $remember = true;

        if ( $remember ) {
            /**
             * Filters the duration of the authentication cookie expiration period.
             *
             * @since 2.8.0
             *
             * @param int  $length   Duration of the expiration period in seconds.
             * @param int  $user_id  User ID.
             * @param bool $remember Whether to remember the user login. Default false.
             */
            $expiration = time() + apply_filters( 'auth_cookie_expiration', 14 * DAY_IN_SECONDS, $user_id, $remember );

            /*
             * Ensure the browser will continue to send the cookie after the expiration time is reached.
             * Needed for the login grace period in wp_validate_auth_cookie().
             */
            $expire = $expiration + ( 12 * HOUR_IN_SECONDS );
        } else {
            /** This filter is documented in wp-includes/pluggable.php */
            $expiration = time() + apply_filters( 'auth_cookie_expiration', 2 * DAY_IN_SECONDS, $user_id, $remember );
            $expire     = 0;
        }

        if ( '' === $secure ) {
            $secure = is_ssl();
        }

        // Front-end cookie is secure when the auth cookie is secure and the site's home URL uses HTTPS.
        $secure_logged_in_cookie = $secure && 'https' === parse_url( get_option( 'home' ), PHP_URL_SCHEME );

        /**
         * Filters whether the auth cookie should only be sent over HTTPS.
         *
         * @since 3.1.0
         *
         * @param bool $secure  Whether the cookie should only be sent over HTTPS.
         * @param int  $user_id User ID.
         */
        $secure = apply_filters( 'secure_auth_cookie', $secure, $user_id );

        /**
         * Filters whether the logged in cookie should only be sent over HTTPS.
         *
         * @since 3.1.0
         *
         * @param bool $secure_logged_in_cookie Whether the logged in cookie should only be sent over HTTPS.
         * @param int  $user_id                 User ID.
         * @param bool $secure                  Whether the auth cookie should only be sent over HTTPS.
         */
        $secure_logged_in_cookie = apply_filters( 'secure_logged_in_cookie', $secure_logged_in_cookie, $user_id, $secure );

        if ( $secure ) {
            $auth_cookie_name = SECURE_AUTH_COOKIE;
            $scheme="secure_auth";
        } else {
            $auth_cookie_name = AUTH_COOKIE;
            $scheme="auth";
        }

        if ( '' === $token ) {
            $manager = WP_Session_Tokens::get_instance( $user_id );
            $token   = $manager->create( $expiration );
        }

        $auth_cookie      = wp_generate_auth_cookie( $user_id, $expiration, $scheme, $token );
        $logged_in_cookie = wp_generate_auth_cookie( $user_id, $expiration, 'logged_in', $token );

        /**
         * Fires immediately before the authentication cookie is set.
         *
         * @since 2.5.0
         * @since 4.9.0 The `$token` parameter was added.
         *
         * @param string $auth_cookie Authentication cookie value.
         * @param int    $expire      The time the login grace period expires as a UNIX timestamp.
         *                            Default is 12 hours past the cookie's expiration time.
         * @param int    $expiration  The time when the authentication cookie expires as a UNIX timestamp.
         *                            Default is 14 days from now.
         * @param int    $user_id     User ID.
         * @param string $scheme      Authentication scheme. Values include 'auth' or 'secure_auth'.
         * @param string $token       User's session token to use for this cookie.
         */
        do_action( 'set_auth_cookie', $auth_cookie, $expire, $expiration, $user_id, $scheme, $token );

        /**
         * Fires immediately before the logged-in authentication cookie is set.
         *
         * @since 2.6.0
         * @since 4.9.0 The `$token` parameter was added.
         *
         * @param string $logged_in_cookie The logged-in cookie value.
         * @param int    $expire           The time the login grace period expires as a UNIX timestamp.
         *                                 Default is 12 hours past the cookie's expiration time.
         * @param int    $expiration       The time when the logged-in authentication cookie expires as a UNIX timestamp.
         *                                 Default is 14 days from now.
         * @param int    $user_id          User ID.
         * @param string $scheme           Authentication scheme. Default 'logged_in'.
         * @param string $token            User's session token to use for this cookie.
         */
        do_action( 'set_logged_in_cookie', $logged_in_cookie, $expire, $expiration, $user_id, 'logged_in', $token );

        /**
         * Allows preventing auth cookies from actually being sent to the client.
         *
         * @since 4.7.4
         *
         * @param bool $send Whether to send auth cookies to the client.
         */
        if ( ! apply_filters( 'send_auth_cookies', true ) ) {
            return;
        }

        setcookie( $auth_cookie_name, $auth_cookie, $expire, PLUGINS_COOKIE_PATH, COOKIE_DOMAIN, $secure, true );
        setcookie( $auth_cookie_name, $auth_cookie, $expire, ADMIN_COOKIE_PATH, COOKIE_DOMAIN, $secure, true );
        setcookie( LOGGED_IN_COOKIE, $logged_in_cookie, $expire, COOKIEPATH, COOKIE_DOMAIN, $secure_logged_in_cookie, true );
        if ( COOKIEPATH != SITECOOKIEPATH ) {
            setcookie( LOGGED_IN_COOKIE, $logged_in_cookie, $expire, SITECOOKIEPATH, COOKIE_DOMAIN, $secure_logged_in_cookie, true );
        }
    }
endif;

Polecam na przykład umieścić to we wtyczce MU wp-content/mu-plugins/always-remember.php