Did you check the Large Scale Deployment Guide on this? There is section dedicated to Registry settings which will also allow you to disable the Check For Updates feature (see screenshot below):
The problem is that I can't set a registry key in HKEY_CURRENT_USER as a setting for all users on a computer. It must be set in HKEY_LOCAL_MACHINE as far as I know.
I can't find any description in the manual to handle it as a global setting.