[SR-Users] Include parameters in replies

Greetings, I need to to include some routing information (Two Id's, example "id_in=10;id_out=72") to be read later by Kamailio in every Request (Except the first one and in every Reply. For the requests, i'm including this info as parameters in the Record-Route and i'm reading it later in the Route Headers. For replies i thought about using the Via header. I'm using subst_hf() and i'm having success adding the parameter to Via in the requests. However, it does not seem the best idea since i breake the routing when i add the parameter. I wanted to avoid using custom headers for this since i can't really be sure that they won't be erased by any client's CPE or endpoint. Any ideas on this ? Thanks Cheers, Duarte Rocha