Hi, AFAIK kamailio does not add Path header for a REGISTER that is routed to another server. Adding it should be straightforward:
There is no need for a new script function. Instead use the existing loose_route() function, but:
If the request method is REGISTER then add Path header(s) instead of Record-Route header(s), which the exact SAME value (this includes Outbound flow token and ;ob param, when implemented). No more.
Cheers.