Question about a four-wheel Portable Moving Car project

Hello everyone, I am going to make a four-wheel portable moving car using arduino uno board. The basic idea is that this car should be controlled just like a two-wheel self-balanced car, that is if a person stand on the car and the car is running, his body leans left, the car will sense it and turn left. I am wondering, as the car has four wheel, it is already balanced, so the movement of the body could not change the center of gravity, so the gyroscope used in the two-wheel self-balanced car could not work. How can the car sense the leaning of the people's bodies.

Everybody please give me some ideas and the items I should use. Thank you all.

Perhaps you could have pressure sensors under the rider's feet?