[Users] Prevent bandwidth lost

Hi, I'm wondering how to prevent bandwitdh lost with (open)SER+MediaProxy in this type of network configuration: UA0 --- [(open)SER+MediaProxy] --- [ Internet ] --- [ FW/NAT ] --- [UA1, UA2] UA1, UA2 are one the same network and they are registered in the (open)SER server. If UA1 call UA2 with default media proxy configuration, the RTP flow will not be direct between this two UA. So I lost twice bandwith (from SER to UA1 and SER to UA2). How can i prevent this ? On the REGISTRAR process, I think I could store the public IP used by UA1 and UA2 and the two private IP of this UA. Since they have the same public IP but a different private IP, on the INVITE procces I suppose it's could be possible to indicate that RTP flow can be direct between this two devices, no ? Now which tools (modules) could be used to resolve this ? Thanks, Christophe