Hi Derrick,
Edge Proxy adds a Path header with a flow token and includes the "ob" parameter when Processing Register Requests.
Eg: Path: sip:VskztcQ/S8p4WPbOnHbuyh5iJvJIW3ib@ep1.example.com;lr;ob
http://kamailio.org/docs/modules/stable/modules_k/path.html and http://kamailio.org/docs/modules/stable/modules_k/registrar.html#id2954403 (and the two following params) might be sufficient if you're just interested in traversing NAT via kamailio acting as a load-balancer. It's an implementation of RFC3327, see http://openser.org/pipermail/devel/2006-March/002142.html for a real-world example.
It won't handle the "ob" header and various keep-alive mechanisms proposed in RFC5626 though, but probably you can solve this with the nat-ping features of nathelper or nat_traversal modules anyways?
Andreas