[Freeswitch-users] Strategies for reliably detecting nat on B-leg?

Hey All, I know FreeSWITCH has the agressive-nat-detection parameter for sofia configs which will detect NAT on an incoming call. So we know if the A-leg is natted. The question is, are there any reliable ways to detect nat at the destination before bridging that call? One could assume that if the destination is a gateway, then it would be okay to bypass-media. Also, one could check the sofia registry and assume that if an endpoint is registered to FreeSWITCH that it is NATted and therefore no point in trying to bypass media. But neither of these options seems 100% reliable. Thoughts? Suggestions? Thanks! Bill W.