[Plugin: Author Avatars List] Template tag show only active users

Hi,

How can I show only active users via the php template snippet supplied below? For example all users with one post or more.

<?php require_once(ABSPATH . PLUGINDIR . '/author-avatars/lib/UserList.class.php' );
                $userlist = new UserList();
                $userlist->hiddenusers = array('admin');
                $userlist->roles = array('Administrator', 'Editor', 'Author', 'Contributor');
                $userlist->link_to_authorpage = false;
                $userlist->user_link = bp_memberpage;
                $userlist->show_name = false;
                $userlist->avatar_size = 50;
                $userlist->order = 'random';
                $userlist->output();
                ?>

Thanks for a great plugin!