I know this has been asked before, but I can't seem to put my finger on the answer, any suggestions of where to look are appreciated.

Freeswitch (Sofia) is rewriting the Conact header on calls originating on a trunk ('inbound' context), routing to another trunk ('outbound' context). None of the calls are from registered users or extensions, this is more of an SBC configuration (LCR).

For example,

incoming to Freeswitch:

Contact: <sip:5122046107@74.37.201.198:5060;user=phone>

I really don't want to modify the from userpary, nor do I want to include gw=trunk_2. I just can't figure out the right syntax or parameter to change it. Is it a parameter in the dialplan, or should I be using a regex on the outbound interface?