OK, here's what I think we must do to have hi-jackable cars...
First, copy a "hijack move" from a GTA game.
Then, paste it to Jimmy.
Associate a command (letter) to the move.
Make so, that the trouble-meter increases when you do it.
Give a behaviour to the adult the car has been stolen from.
THEN, write source-code to make the car drivable.
So, give a baheviour to someone beeing bumped.
I think that's all, but I'm just a little little modder... So I could have forgotten something.