Include that in the calculations. There's a certain absolute sideways g-force (decreasable by slowing or straightening), and a certain absolute downwards gravity. These add up to a single total force. So long as the magnitude is at least 1g, there exists a seat orientation such that the passenger feels 1g toward the seat and something on the back.

How much you can spin the seat without those movements causing problems is an open question.

Airplanes are an encouraging precedent. They often make quite sharp turns at extremely high velocity, but tilt into them such that there's almost no perceived lateral acceleration.