The platform moves up and down to simulate diving and free fall... I can't think of any possible way to safely allow somebody in a chair to experience the full range of motion.
It would be fine to lock the wheels of the chair onto the base, but what is going to hold the person in the chair into it?
A seat belt or smaller lap bar? I've noticed that once you're seated there's a sort of shield over your lap that doesn't allow you to fully stand up.