This is what I do when updates are defiantly going on in the background. It prevents the installation of servicing stacks as well. Just keep in mind that you did this so you aren't scratching your head later when updates don't work.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\tiworker.exe]
"Debugger"=">nul 2>&1"