You cant... Ultimately Untangle routes traffic based on the IP address. The login process is just filling a table of names to addresses that the device then uses to route. It will take some light proxy/session tracking with cookies to make it truly user driven. To be honest that's the next logical step, and along the way Untangle will likely end up with a caching proxy too.
CP doesn't change user based policies... All it provides is another way to build that ad table.