Well, it was impromptu mod time tonight. On the way home I decided I had enough keying off and decided it was time for a kill switch. When I got home, I grabbed my electrical diagrams and found the crankshaft position sensor wire off the ECU.
I snipped it and soldered on wires.
Brought the wires up through the shifter boot and soldered on a normally closed momentary switch that interrupts the crankshaft position sensor signal.
For now, I just taped it on. I'm not sure where I really want it yet, but this looks like a good spot. I can reach it with my thumb, but its not really in the way if I grab the shifter.
I tried it out a few times in the driveway. It works great. I do think I want to put another switch in parallel with it to make an override for when other people drive the car so they don't have to worry about killing the engine.