I'm not sure if this will 100% work for you, but keep restricting the C drive, but simply use Folder Redirection...
to redirect the My Documents folder to the network. Because things aren't being preserved on the C drive anymore (because they're now being redirected to the network) you may get what you're after.
Related Q&A from Jeremy Moskowitz
How can I restrict rights for a group of users on a specific OU of computers, but not on any compute
Expert Jeremy Moskowitz shows a reader how to use loopback policy processing to restrict rights for a group of users on a specific OU of computers.continue reading
Expert Jeremy Moskowitz shows a reader one of the best ways to set permissions for a new user in Group Policy.continue reading
Expert Jeremy Moskowitz explains how to use Group Policy for a Windows 2000 Server to apply proxy settings automatically on all the workstations in a...continue reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.