[Users] Stateful Transfers

I got a big problem here that I don't know how to fix. An OpenSER system forwards calls from phones to Asterisk boxes. Up until now we had been using the dispatcher to evenly distribute calls to the Asterisk boxes. However, when someone transfers a call, using the dispatcher, the call can go to a different Asterisk box, which breaks the transfer. I need to find some way to make OpenSER route transfers to the same Asterisk system. I'm not sure how to do this. If there was some way to, upon an INVITE, check and see if there was already a call in progress for that user and then send it to the same Asterisk system. Would stateful processing help in this way? Can stateful processing 'remember' that there's a call already in progress like this, or does the stateful simply relate to stateful processing of a single call from INVITE to OK/ACK? Doug.