First of all, I didn't search for this suggestion so it may have been posted already.
How about UTAN links a GUID and the IP of the player together to create one ID? This would be bad if it'd happen automatically since people might share their copy's for example... But what if it was optional? Here's the scenario - Somebody with a stolen key appeals in these forums after which we can see a large amount of IP's from all over the globe. After that you match the IP used to post with an IP from the UTAN database (That's then posted automatically). If there is no match then the user might be using a proxy, you'd have to ask him/her then. After the GUID-IP are linked then a new ID will be created, and with THAT he/she can play on UTAN servers.
Also, it would probably be a good idea to compare the IP used on the server when the aimbot was used with the user posting the appeal.
Sorry if this makes like no sense at all, just a thought.