I've taught that exact same exercise but I would create an out-of-trim force for a low speed situation (trim nose up). That way, I could keep my hand against the yoke to stay level, and guard the yoke against moving back too much by keeping my hand near it. It is much easier to just move your hand back half a centimeter once the student has applied enough pressure, you are then in a good position to reapply force to the yoke if the student releases it inadvertently.