How to modify author base slug with groups and slug to use nice_nickname?

After reading the following suggestions from Jan Fabry regarding URL rewrite and the author slug I took the challenge in combining both solution in one.

• Change author base slug for different roles
• Change the author slug from user name to nickname

Goal: The goal of this is to have a structure for the authors as followed:

http://domain.tld/employees/(department|group)/firstname-lastname

Current solution: In order to arrange this I have merged the solutions as mentioned in the referred answers as followed:

// NOTE: This need to be stored different and need to be attached to author/profile
//       Will be added to user settings so this can be changed (only primary group will be stored)
$wpa04142013_author_groups = array( 'staff', 'admin', 'support', 'itnerds', 'etc' );

/*
 * Init WordPress to add globals which can be used for the authors and levels of the authors.
 */
add_action( 'init', 'wpa04142013_init' );
function wpa04142013_init()
{
    global $wp_rewrite;
    $author_groups = $GLOBALS['wpa04142013_author_groups'];

    // Define the tag and use it in the rewrite rule
    add_rewrite_tag( '%author_group%', '(' . implode( '|', $author_groups ) . ')' );
    $wp_rewrite->author_base="employees/%author_group%";
}

Above solution will make sure the author_base is changed as needed based upon the goal defined in the beginning. After that the author_link needs to be hooked in other to use the correct link to the author archive page.

add_filter( 'author_link', 'wpa04142013_author_link', 10, 3 );
function wpa04142013_author_link( $link, $author_id, $author_nicename )
{
    //NOTE: This if/else needs to be changed --> either select case and use
    //      global defined groups based upon user property
    if ( 1 == $author_id ) {
        $author_group = 'staff';
    } else {
        $author_group = 'admin';
    }
    $link = str_replace( '%author_group%', $author_group, $link );

    //Below solution added from other WordPress Answers suggestion
        $author_nickname = get_user_meta( $author_id, 'nickname', true );
    if ( $author_nickname ) {
        $link = str_replace( $author_nicename, $author_nickname, $link );
    }

    return $link;
}

After implementing above the link to the author is working correctly, but the request and url rewrite is not working. Clicking the link of the author will result in a 404 page for the template.

If I am not mistaken I also need to modify the following section, but this is where it is going wrong.

/*
 * Hook into 'request' to modify the author request.
 * Change the way the lookup works (via nickname in stead of the slug)
 */
add_filter( 'request', 'wpa04142013_request' );
function wpa04142013_request( $query_vars )
{
    if ( array_key_exists( 'author_name', $query_vars ) ) {
        global $wpdb;
        $author_id = $wpdb->get_var( $wpdb->prepare( "SELECT user_id FROM {$wpdb->usermeta} WHERE meta_key='nickname' AND meta_value = %s", $query_vars['author_name'] ) );
        if ( $author_id ) {
            $query_vars['author'] = $author_id;
            unset( $query_vars['author_name'] );   
        }
    }
    return $query_vars;
}

add_filter( 'author_rewrite_rules', 'wpa04142013_author_rewrite_rules' );
function wpa04142013_author_rewrite_rules( $author_rewrite_rules )
{
    foreach ( $author_rewrite_rules as $pattern => $substitution ) {
        if ( FALSE === strpos( $substitution, 'author_name' ) ) {
            unset( $author_rewrite_rules[$pattern] );
        }
    }
    return $author_rewrite_rules;
}

I have already gotten some help on the Dutch WordPress support forum, but I am still stuck in finding the right solution. Also looked into the rewrites with the Rewrite Analyzer, but could not find the author_group. Hopefully you can help me pointing me in the right direction.

Edit: previous answer not working. Following solution does not provide sanitized nicknames, but should do the trick:

    $nn = urldecode($query_vars['author_name'] );
    $author_id = $wpdb->get_var( $wpdb->prepare( "SELECT user_id FROM {$wpdb->usermeta} WHERE meta_key='nickname' AND meta_value = %s", $nn ) );