They'd never do it but I imagine a system that was loud, flashy, and embarrassing, that activated when autopilot is misused (i.e. auto-pilot is demanding user intervention and intervention is not given) would be most effective in incentivizing drivers to change their behavior.

I.e. a loud beeping noise that annoyed pedestrians and other drivers until you took the wheel. Kind of like how accidentally triggering your car alarm in the parking lot will lead to a very hasty correction on your part.