Seeing how expensive the topper is, lord know how much a lockdown bar with a button would be...
Adding it to the start button would be an easier solution. But at the end of the day I would bet you see a software fix where on the pro the X shot kills more walkers, multikills actually kill more walkers or the amount of walkers required to kill to reach Last Man Standing is reduced a little. I am fine with how hard it its, a game loses some of its "one more game" appeal when you can get to the wizard mode regularly.