[SR-Users] Call forking priority

I have a proxy that manage fix calls and a proxy that manage mobile calls. I want to implement call forking so when I call to a fix phone the call goes to the fix proxy and it forks to the mobile proxy who manage the call and viceversa. I want the fix to ring 2 or 3 times before the mobile. In order to do so I relay first to the fixed proxy, which will bounce back to mobile proxy the branch for mobile device. But now if I want to be able to choose which phone (mobile or fixe) rings before I have tried by doing the "async_route("RELAY", "7");" in the fixe proxy like in the mobile proxy but it doesn't work.