$REMOTE_IP in Contact URI (or Alternative) BCP

Hello,

 

We are front-ending our Metaswitch CFS with an HA pair of 3820s with registration caching enabled.  It would be useful if our support staff could tell what the original public IP of an IAD was by looking at the registration in in our switch or at some header in our capture server, as right now all they see is the IP address of the core interface on the SBC.  Is there a best practice method to include this information in the contact URI or anywhere else in the SIP packets via an HMR?  If not, is anybody out there doing