As you know, to create a manditory profile, you rename the user's NTUser.dat file to NTUser.man. To prevent these users from logging on when the server is off-line:
1. Rename the profile folder to include a .man
2. In User Manager for Domains, change the User's Profile Path: to reflect the .man extension
Example: If Jennifer's profile path was \\Server\Share\Jennifer\Profile, change it to \\Server\Share\Jennifer\Profile.man and reflect that change in the User Profile Path: entry of User Manager for Domains.
With these changes, Jennifer will be prevented from logging on during those rare server outages.