As you're aware, SWG5.2 supports Win2012 for neither DCInteface nor NTLM authentication of users:
http://www.symantec.com/docs/TECH203506
This essentially means that you have no supported method at this time of determining which user is doing the browsing (so identification by hostname/IP address only). As a partner, I'd suggest feeding this back through your Symantec contact.
You may try getting NTLM to work, just be aware that it won't be supported.