[SR-Users] Is it possible to replace Request-URI in the REGISTERs with the result of dispatcher?

Hello, I build three kamailioes, one acts as a pass-through proxy as well as load-balancing, the two registrars. The kamailio_1 decides to which registrar the REGISTER should forward by a dispatcher based on db_text. ----->kamailio_2(IP2, registrar) SoftPhone--->kamailio_1(IP1, pass-through proxy)--| | ----->kamailio_3(IP3, registrar) | dispatcher(db_text) I expect the kamailio_1 forward the REGISTERs to kamailio_2/kamailio_3, and kamailio_2/kamailio_3 respond with 200 OK. But in fact, the registrars send the REGISTER back to kamailio_1. I think the reason is that the host part of Request-URI in REGISTER from SoftPhone is IP1, and kamailio_1 does not rewrite it as a pass-through proxy, so kamailio_2/kamailio_3 will find the host in Request-URI is not mine, thus route the REGISTER back to kamailio_1 according Request-URI. The setting of SoftPhone cannot be changed, so is it possible to : 1) replace host part of Request-URI in the REGISTERs with the result of dispatcher in kamailio_1 , or 2) force kamailio_2/kamailio_3 to respond rather than forward? Thanks!