I found a solution that works just great. I already do a preg_split on the $username attribute, so after I run that, this is what I've done to unset administrator usernames from the $username attribute:
$users = preg_split("/[\s,]+/",$username);
wp_get_current_user();
if(current_user_can(administrator)){
$nohidename = array_search($current_user->user_login,$users);
if($nohidename !== FALSE){unset($users[$nohidename]);
}
}
So it does it just based on whether the current user is an administrator. If not, it leaves it as is. Works great.
EDIT - An even simpler way to do it, without the array_search:
if(current_user_can(administrator)){
if($username){
unset($username);
}
}