I have an interesting NAT setup. I'm running FS on the inside of our network as a router/proxy between some SIP phones and DID providers. However, each DID provider is behind a *different* NAT (a property of our VPN setups for them). 

For instance: DID1 is at IP 192.168.1.1 and DID2 is at 10.0.0.1. 

I have calls working for each of them when I set the following in my external profile:

However, I need to dynamically route between *both* of them. I need a mechanism for setting ext-rtp-ip and ext-sip-ip in the dialplan itself! 

Is there a set way to do this? 

Thanks!