[Freeswitch-users] using ip and port from contact

Hi all. I have a freeswitch sitting on a public IP that has a multitude of devices, mostly spa2102s, spread across the country, all behind routers. Our 8xx voip supplier (iristel) sends us traffic on port 5060 but their switch is behind a firewall. As a result I receive traffic from them on any port the firewall chooses but they want the response to be to port 5060, which is of course in the contact message. This is trunk group is authorized by IP address. Is there a setting I can do that will allow me to return the traffic to them on the ip and port in the contact but not louse up the normal nat traffic from the atas. Darcy