[SR-Users] Force signalling??

Hi, I'm trying to setup an inbound proxy (Proxy-1) using dispatcher to relay between 2 other proxies (proxy-2 & 3) depending on DID, but I need to force all signalling through Proxy-1. so #2 & 3 only communicate with #1 and #1 only communicates up and down stream. My trouble is, the INVITES contain the original $ru $fu $tu & $ct info when passing down to Proxy-2 or 3. The result is, only partial signalling is being sent to Proxy-1. After the ACK it seems that Proxy-1 is removed from the communication path entirely as $ru becomes $rU@proxy-2 in the ACK from upstream so Proxy-1 is out of the picture from then on. This means BYE's are not working as Proxy-2 & 3 do not have authentication upstream. I suspect that I need to re-write $ru $fu $tu & $ct info on the original INVITE to reflect Proxy-1 information before dispatching. Is that what I'm missing? If so, how would I restore the original INVITE info to send upstream again on replies etc.? Any help is greatly appreciated. Tia, Skyler