Ah, ok.
Well, I do not really have an idea as it looks like you have already googled the whole Internet 
So I may assume you have seen the old thread here: Multi-Server Umgebung - GPO - selbsterstellte OU ?
If you use as filtering rule the computers, not the users? No way?
BTW: With UCS@school did you buy support? I would suggest to create a support ticket in case you do not find a solution.
/KNEBB