User collision/duplicate users and mysql backend

I was wondering, any change of getting the User collision/duplicate users option in to the sql module (pref. mysql) ?? I'm still trying to get the mysql backend to work, with duplicate usernames. (still stuck here) in the tuning guide, i found a document called 'tuning guide' under the sql module section, it says something about 'multi column index' and 'sql for double login detection' ? but what is mend with this ?? the problem is that i have (a few) users with 1 username and multiple computers. we filter on username and calling-station-id (MAC). but somehow the mysql backend can't handle this (tell me if I'm wrong!!) any solution is welcome... Cheers Collen