Bump - I also was concerned about the idea of 'public' situations with the owner nearby (family get together, car show, etc) but untrained people might be in the car so you'd like all aspects of the car to operate (screen, air, stereo) to allow showing-off, but NOT allow the car to move.
So, I designed and built an immobilizer device.
It's a small fob (smaller than the car fob) that plugs into the charge port - you insert it and close them charge port, and then when you continue to stay nearby the car can't go (it thinks the car is about to charge). Obviously you don't need this immobilizer gadget if you are near a real charging port with power (like your garage).
I thought that Tesla themselves would like it, for their stores - instead of a big charging cable, you'd just pop this in. But, the feedback was that they didn't want to use it.
Just a little 'product idea failure' story.
David