You could easily wire a magnetic reed switch to the DSP2 input on a LB7 instead of a regular switch or keyed switch. I would also do the DSP2 setup, especially if you want to get EFILive anyway.
Ben (duratothemax) retrofit PassKey 3 onto his GMT800. That uses a unique coded transponder inside each key, and is much harder to bypass than PassLock 2 that is used on the GMT800 normally. He is almost impossible to get ahold of, so I am going to try and figure out how to retrofit it onto my LB7 this summer. If I get it working, I'll do a writeup. But be warned, I suspect it will not be an easy conversion.
Midnight, for the specific situation you're in, how are the thieves stealing the trucks? Are they getting new keys cut off the VIN by a dishonest locksmith, or are they brute forcing the ignition switch? If they are getting keys made from the VIN, you can find someone else with a GMT800 and swap all your lock cylinders & keys with them. Then your locks won't match your VIN, and a key cut to your VIN won't run your vehicle.
My brother and I keep contemplating this strategy, but I think the PassKey 3 conversion would be even better (couldn't just force the ignition with that), so I am going to try that first.