2008 R2 RDS File Association Problems

I've tried multiple methods of associating .tif files with either Microsoft Office Document Imaging or a custom program created by a insurance software vendor we use.  Neither will work.  I've tried using the assoc command and Group Policy Preferences.  We still have a 2003 DC, and this is our first 2008 R2 RDS machine.  User choice works, and I'd really like to avoid having to connect to every session and change their default TIF viewer if at all possible.  I've followed every guide I can find and this is driving me nuts.  Any ideas what could be going wrong?  I've tried applying the policy to the computer OU as well as the user OU with no luck.