Map Network Drive with GPO Preferences

Hi!

While trying out GPO Preferences in the new Windows 2008 Server I came across a little problem.

I wanted to map a network drive with a path containing a users username. For example "\\fileserver\%USERNAME%\".
Using that path didn't seem to work though, which i guess means the function does not resolve environment variables?
Is there any other way around this without having to use logon-scripts?

Thanks for all help!

/PB