There are a few ways to have a kill switch but if someone wants to steal your car, they can always put it on a flatbed and drive it away.
I think that some of car thieves, they don't always have a flatbed with them (probably the professional car thieves ), Most of the time they just brake your window and hot wire the ignition switch and off they go, at least that is what I read or see on T.V.,, I may be wrong on this.
The reason, I would like to do the kill switch install in my TDI, is that just in case I happen to be in a bad area and you are forced to park your car there for a little while, or any other place that you may park for long periods of times, just for a piece of mind.
Excellent suggestion from both of you, about splitting the imobilizer, but I do noteven have the slightest idea where the wires are, I have never done this in any car, so what you are suggesting is the way to go, instead of splitting the live wire at the fuel pump,,, I will wait to see if Chittybangbang could come up with anything on this, thank for your info so far.