Valet tune or something

So this may seem stupid to some of you, but... I have a LBZ in a 2003 Suburban and I am probably a little over concerned about it getting stolen. My insurance wouldn't pay out what I have into it and truck theft is pretty common around here.

Since I have a DSP5 switch and EFIlive it seems like you could make a tune that would run like crap, maybe only do 10 mph or something almost like limp mode. I figure if you had a DPDT relay you could interrupt the DSP5 switch so that it stayed in "Tune 1". You could then have a momentary button that would trigger the relay and one set of contacts would complete the DSP5 wiring and the second set of contacts would hold the relay open. If you used a Ignition + wire for the relay coil then it would interrupt the relay every time you shut it off. You could all kinds of creative with where you mounted the button or what it looked like.

My question is: What would be a good way to make "Tune 1" run like crap without effecting the other tunes or hurting the engine? I was thinking something like setting the pedal vs desired torque (or whatever it is called) to something really low, like barely over idle. What does limp mode do?

Thank you