JR at the Stellarparthenon BBS came up with the following to turn it off:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINESOFTWAREPoliciesMicrosoftWindowsWindowsUpdate]
"DisableOSUpgrade"=dword:00000001
[HKEY_LOCAL_MACHINESOFTWAREPoliciesMicrosoftWindowsGWX]
"DisableGWX"=dword:00000001
I haven’t tried it myself, but feel free to try this out.

You past this into a text document, and give it the .reg extension, and it will run when you double click on it.