We have added an initial solution for this issue in Chrome 42. Users can set the following preference:

"webrtc": { "multiple_routes_enabled": false },

For the location of the prefs file, see http://www.chromium.org/administrators/configuring-other-pre....

This forces all WebRTC connections to only use server-reflexive and relay ICE candidates, and only on the default IP route. While this may cause a QoS hit (two users behind NAT can no longer keep their traffic internal to the NAT), it does allow the issue mentioned here to be fully addressed without disabling WebRTC altogether.