[Serusers] Communication between SER as Proxy and a SIP Server

Hi, I need to configure SER as a SIP proxy and that all SIP requests go through SER. To do it, you normally add SER as an outbound proxy into a routing table in your SIP server. But actually I can't modify the server... So, the solution I wish to implement is a way to register SER in SIP server as an "UAC" when it receives a REGISTER request from a real one. So first things first, is it possible ? I think you could do it by doing the following : - Save UAC real location. - Rewrite Contact Header Field in SIP packet request with SER IP adress and forward this request to SIP server. Then when you receive a request from SIP server, SER searches for UAC real location and forward request to it. So finally, how could you do it ? I tought I could use subst() function but it seems I can't master this function perfectly to make it work. So does anyone have an idea ? Thanks, Anthony