I'm not sure if it possible at all.
Anyway, let see a real case.
We have Head Office (HO) and two small branches, A and B. We have VPN tunnels between HO and branch A, and between HO and branch B.
We HAVE NOT VPN tunnel between branch A and B. VPN router CANNOT route VPN traffic between A and B, and we not need this.
But we need that calls will pass between HO and A, HO and B, and between A and B.
All Extensions at branches A and B registered directly on HO 3CX Server.
Currently, if I want to call from A to B, I have to enable PBX Delivers Audio in Extensions properties in branch A, or branch B, or both of them. So, the RTP stream will always pass via HO 3CX Server.
But when A or B calls to HO, I dont want to pass RTP via 3CX server, because I have direct VPN tunnel, and this put additional load on the server.
So, it will be great, if Extensions in branch A or B will automatically choose to proxy the RTP stream.
In other words, if call between A and B cannot be send in Bypass mode, 3CX will force the endpoints to sent RTP via 3CX server (in PBX Delivers Audio mode).
I hope my explanation is clear
