Direct Access on Windows Server 2012 - Limit users

I'm testing DirectAccess with a Windows 2012 server in Single NIC configuration and Windows 7 clients.
All is going well so now is time to tighten it up a bit.
I've limited the ability for a machine to connect with security groups - part of the setup wizard so quite easy.
I'd like to ALSO be able to limit the users who can login WITHOU preventing their machines from still connecting
I found this old post
http://social.technet.microsoft.com/Forums/en-US/windowsserver2008r2networking/thread/89ce2825-4fa8-44e1-a3ad-dd6fe6c52fea
and could configure the first part of the answer, but not the second - it's read-only so I can't get a response that way.
How do you exactly configure the second part of this answer, OR, with server 2012 as the DA server, is there an even easier way?