I think you're right not wanting to let Ben get whip dependent. What I would do is practice getting him to move of the leg as responsively as you can while you are carrying the whip so he gets used to moving of on slight pressure. Then start doing the first half of your ride with a whip then gradually stop using it towards the end. After a while he may get used to just moving of that he forgets about the whip. If he is not being responsive demand that he is, with a tap from a whip or whatever you chose to do. Continuse kicking or heavy use from the legs often makes the situation worse as they just grow used to it.