There's currently no way to disable it at all, but you can stop this annoying window from popping out.
Also, you probably have noticed that the process is "wuactl.exe", and you can't just kill it: it comes again.
Install Process explorer from SysInternals: it's capable of 'suspending' a process for debug purposes.
Find 'wuactl.exe' there, right-click, and choose 'suspend'. The process will not display anything after this trick :)
I;m not sure whether each user has this process running, but being an Administrator you can suspend all of them. Make sure the popup window is not visible, or the user won't be able even to dismiss it temporarily!
A few words about automating this: 'suspend' action is WinAPI-dirven, so you can create a small daemon (or maybe even a bat script?) that determines whether 'wuactl.exe' is running, and suspends it if found.