[Falcon4.0]

"If someone got access to the car for a time, maybe only a few minutes, relatively simple wirelessly controllable devices could be installed that would override the driver’s control of the throttle and possibly also the electric power steering assist."

Actually it's quite easier than that.
Just drop in a re-programed CPU which would be instructed to go full throttle after the car reaches, say 50 mph indicating that it is on a highway.
And from my understanding you can also disable the transmission from changing gears.

[UCANSEE2]

Just drop in a re-programed CPU

The car computer is not usually EASILY ACCESSIBLE. If the car was in the shop, one COULD replace the entire computer BOX, but not the individual CPU chip.

HOWEVER, IF one could gain access to the interior of the car without setting off the alarms, all one has to do is drop in the proper CD into the CD player.