I understand your problem (and have a similar one)! Unfortunatley, I do not have an answer...
I do know that if you insert multiple instances of the same sub-assembly, all instances will be driven with the same constraints. However, I have not found a way to have them constained in the main asembly (for placement) and actuate, even if they are to have the same drive constraints.
I'm still working on it and if I have any luck I'l let ya know!!