[SR-Users] How to get branch id on reply route

Hi, I'm trying to implement parallel call forking scenario. Since target clients have different media profiles, I need to set different rtpengine options for those forked calls. So according to the rtpengine module documentation, I set via-branch option on request and response, '1' and '2' respectively ('auto' option is not working. There is no code implementing this parameter). However all forked branches have the same via branch id which is the incoming INVITE's via branch id. As a result, rtpengine thinks that all the offers belong to the same session I guess. It seems I have only 'extra' option with extra_pv_id variable. In order to use it, I need an elegant way to differentiate forked branches in request and response processing. I would appreciate any suggestion.