Best thing you could do is forget about the "snap roll switch" and learn to do the maneuver. Setting up that switch will handicap you forever. If you do it, there is only one flight condition where it will work. One speed, straight and level, one direction.

The control inputs for a snap roll vary considerably from straight and level if you climb, change speed, roll in the opposite direction and so on. That switch is just a crutch that will keep you from learning the basically simple control inputs for a snap in all sorts of flight modes.