Well, I did say I'd report back regarding this hack. After a few hiccups I finally got it working with no problems.
However, on a test install using vBulletin 3.6 beta 1 doesn't work, you cannot save settings in AdminCP.
I tried again but under vBulletin 3.5.4 on another test installation, and voila it worked first time. This is one mod I would like to see in vBulletin 3.6 - when the full version is released.
Nice work! Now I'll click install..