I already suggested breaking the power feed to the ECU. Screwing with he dist. leads is likely not a great idea. They are a "low signal" circuit, subject to interference pickup.
I was a little worried about this too, but mine has been running fine this way for awhile. The leads to the dist pickup are pretty long already, so a few more feet of wire doesn’t see to have any effect. I would be surprised if anybody could steal mine (without a tow truck) even if you had the keys. It is impossible to hot wire this way.
I also added an electric door lock solenoid to the console shifter so it won’t come out of park like a late model car. Like others have said, I don’t know that this will stop anyone, but should slow them down if they don’t have a tow truck. I wanted to do something odd & unexpected.