Stewart did a great driving instruction video for Ford back in the 80s, called "Behind the Wheel'. There was a cool bit where they attached a wide, shallow bowl to the hood of a car and put a ball in it.
Same idea. Do a slalom, including starting and stopping, and don't let the ball fall out.
Sometimes when driving I think about that and try to stop so gently that if I had one of those on my car, the ball would still be in the bowl. You have to modulate your brake very carefully, reducing pressure as the car comes to a halt until you're barely touching them. Otherwise the car jerks a bit.
The whole hour-long video is well worth watching (and has some great historical race footage), but the ball-and-dish bit starts at about 43:00
Link to original page on YouTube.