[Serusers] append_branch Question

I must be missing something; This seems like it should be so simple. I am trying to have ser 0.9. parallel fork using append_branch which I can get to work with the following append_branch("sip:voicemail@xxx.xxx.83.5:5060"); t_relay(); it Invites the original uri and then new one spec'd in append branch but what I need is to have the the original invited and the append branch keep the original user portion and change the host and port portion but I don't seem to be it seem to be able to find a way to accomplish this. What am I missing! Example: Ua1 and Ua2 are both registered with SER and Ua1@ser calls Ua2@ser then ser needs to Invite ua2@usrloc and ua2@asterisk Thanks