routing question

How do I redirect a call out the same realm that it came in on, based on the calling number?    We are routing an inbound toll free number throught the SBC through Avaya Session Manager  to an IVR.  The IVR will dial a number that gets sent

to a sip server through Session Manager.   This sip server will issue a refer back to the SBC which will need to turn the call back around to the Session Manager and to our ACT PBX.

So the question is that when the refer goes back to the SBC, how do I route the call back through the same Realm that it came in on.  Our local policy currently comes in one Realm, and out the realm to the provider.   How do I add to this local policy to send from a specific number back out the inside-xo realm?   Thanks! LM