Proxy IP Address

I have a situation where all my authentication requests are proxied to me. I have 4 different groups of users that require unique local polieies and have been using a fairly complicated parsing of the Called ID phone number and a couple other fields to figure out which group a request is in. However, I just found out that each of the 4 groups is being proxied through different proxy servers. It would be real easy to distinguish the group from the IP address that the proxy request is being sent from. However, I have not been able to find a variable that contains that information. Have I missed it?