When the car is too good and fast to respond, it will get hit from behind it seems. I guess they could change their algorithm to be slow-reacting. dumbing down machines so that petty humans can catch up.
You'd want to get smarter, not dumber: taking into account the fact that the unpredictable (to the car behind) braking could in itself cause an accident, and calculating a best compromise to avoid both collisions, with priority to the more dangerous of the two (the fender-bender could be a great option if you avoid another car doing 50). I'd be surprised if their software doesn't support this kind of thing already.
The priority will be probably be not to hit the car in front of you so that you're not at fault for an accident.
I'd guess that most from-behind collisions are due to excessive speed for conditions, or driver inattention. Not much that the leading car can do about either of those.
The leading car can do several things in those scenarios, ranging from increased stopping time (which it should already likely be doing to maximize fuel efficiency), brake light usage, or in extreme cases changing lanes to get out of the way.
I hope they already did that, they say they can track all moving agents around, and roboticists know physics so they know they have to dissipate energy as smoothly as possible in the system including all neighbors.