OK, how about %computername%? If you have MS office installed, read
 Code:
HKCU\Software\Microsoft\Office\12.0\Outlook\Machine Name
I also found
 Code:
HKCU\Software\Microsoft\Windows\ShellNoRoam\(Default)
and
 Code:
 HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\State\Machine\Distinguished-Name
or
 Code:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\ComputerName\ActiveComputerName\ComputerName
There are many more. I don't have a citrix setup, so I can't really search for any specific entries relative to that.