force RTP via IP Office (Avaya Communicator)

[kirchenlo]

Hallo,
I have a try installation at a potential customer. They just want to use softphones, in this case Avaya Communicator. My problem is that Avaya communicator is always doing the RTP stream direct between the softphones and I would like (the customer wants) that the media returns or goes always via the IP Office server.
This is what is happening
SIP Signalling
Phone A - - - > IP Office - - - > Phone B
RTP (after established call)
Phone A - - - - - - - - - - - - - - -> Phone B

What I need is a cost effective solution that the media travels via the IP Office.
SIP Signalling
Phone A - - - > IP Office - - - > Phone B
RTP (after established call)
Phone A - - - > IP Office - - - > Phone B
Anyone an idea?