The best solution would be some sort of remote terminal or phone at the charging station that could be used to contact police & Tesla. The owner who's car was just stolen (along with his cell) can immediately call for help. Cameras at the charging stations would also be wonderful. You think that Tesla would already have that, just to prevent nonsense.
You wouldn't want the car to lock the occupants inside. As others have said, they would just trash it trying to get out. At best, you'd end up with a broken window. The ideal solution would be to let the car drive away at a reduced power level (you wouldn't want them in "insane" mode, but maybe limited to 30-45mph), just to get the bad guys a safe distance away (maybe 3-4 miles) before the car disables itself. And of course, take photos & video of the occupants. This sounds like a perfect setup for the valet mode.
How to activate this during a dynamic carjack is something I would have no idea... maybe a button that sends a signal from the charging station to the car that had just been charged. You would want an owner to be able to access it even if his phone had been stolen.