Very true about the questionable vision.

Does the person have access to a simulator?

I would teach him to fly with rudder and throttle alone first; after all, that is the proper way to fly basic flights.

He does not need to learn rolls and loops at this stage; hence, the right stick can be left alone until he becomes familiar with proper plane attitude and speed for level flight.

His habit will not be so bad for flaring at landing later on.

Just don't give up on him and introduce him to simulators.