Prevent PST files from being made available offline

As we've begun rolling out new machines to our employees with Windows 7 on them, we've discovered a little problem with our standard configuration.  When using Windows XP, we relocated our users My Documents folders to their H drive (home directory on the file server) and then set the H drive to work offline.  We also stored everyone's PST files in their H drive, but Windows XP was always smart enough to skip the PST files and tell us that files of this type could not be made available offline.  We were cool with that and all was well.  Now we are finding that when we configure our user’s computers like this, Windows 7 is behaving a little differently.  It now thinks that it can make PST files available offline and because of this, bad things are happening.  Users now think that they can access their PST files when they are away from the office and when they come back, the sync tries to happen but never works completely. We're running in to corruption issues and two separate non-identical copies of the same file, one in the local offline cache and one on the file server.  In a perfect world, I would just tell Windows 7 not to even think about touching the PST files and everything would be groovy but there does not seem to be a way to do this.  

Has anyone run into something similar?  Can anyone recommend a solution or workaround?  I’d really appreciate it.  (Also, I am aware of the evils of dealing with PST files and will hopefully be addressing them sometime in the near future)

Thanks!
-Chris