Mingle - Users - Online (example)

gistfile1.php

<?php
/*
Plugin Name: Mingle - Users - Online (example)
Description: Requires WP-UserOnline to be installed
*/

function mingle_linked_names( $name, $user ) {
	if ( !$user->user_id ) {
		return $name;
	}

	$nicename = get_userdata( $user->user_id )->user_nicename;

	return "<a href='http://wpmingle.com/$nicename'>$name</a>";
}
add_filter( 'useronline_display_user', 'mingle_linked_names', 10, 2 );