I'm genuinely curious, as an occasional motorcyle enthusiast myself, whether it's physically possible to counter the movements of the rider in addition to and counter to their movements, which represent a large portion of the vehicle mass. My gut feeling based on the segway is, yes, it's possible. But I'd love to hear any analyses to the negative.
It's probably possible to some extent. It's like having a anxious pillion rider on your bike. I remember when I first took my little sister along on my motorcycle, she'd lean the wrong way in the curves because she was scared the bike might fall over or something. Made controlling the bike harder, but not impossible.
(That experience taught me to always tell people to lean into the curve if they've never sat on a motorcycle before)
My guess is, you could put a 1m vertical pole behind the driver with some mass attached to the top end of it and motors controlling it at the bottom. That should give you enough angular control to compensate for whatever rider is doing.
Given the close interaction between the rider and the bike, I'm not sure how comfortable would such a vehicle be. It may turn out to be nausea-inducing.
I wonder if a "feet first" design would be once solution. The lower centre of gravity should be easier to stabilise. I don't know whether the riding style of an FF makes the same use of the rider shifting their weight as with a regular bike.
