I sometimes have to travel and leave my car for a day or 2 at the airport. I'm wondering if anybody has ever moved the drivers seat all the way forward and locked it there with a padlock? In the fully forward position it looks like you could put a padlock through the holes on the seat rail to prevent the seat from sliding back. I can't imagine anybody could drive the car with the seat all the way forward as there is so little legroom.
Without the key there is no way to drive away with a Prius. It can't be hot wired. The computer needs the code from the keyfob in order to start. No computer...no go. It could always be towed away, but a lock on the seat would not matter anyway. Also I'm sure someone who steals cars for a living would have bolt cutter handy anyway.
This technique also does very little, if anything to identify the car as a poor target. It is better to have them bypass your car all together... than to find it difficult to drive after they bust the window. /Jim
You want the car to be visably difficult to steal. Part of the reason folks the the Club is as a deterrant, not because it is so effective.