Citrix compatible web filtering solution

I’m looking for a Web Filtering solution, either hardware or software, that is compatible in a Citrix / Terminal services environment. The problem I am running into is finding a solution that can filter by username or individual Citrix session. The majority of solutions out there apply filters based on the Ip address of the host computer making the request. Since multiple users will be accessing internet resources from the same Ip address these solutions fall short.

Anybody out there using a webfilter software app / hardware appliance in a Citrix environment? Suggestions?

Thanks
Eric