Unfortunately, only the local users can create or modifiy disk encryption access lists. There is no way to do that from Universal server.
Workaround for this:
users can be added using command line :
c:\program files\pgp corporation\pgp desktop\pgpwde --add-user --disk 0 --user username -p password
c:\program files <x86>\pgp corporation\pgp desktop for 64bit
So if you script this command into a batch file, deploy using Group Policy and schedule time to run , it should make the trick