Ok so I could not find a way around the mentioned limitations with WPF. So what I did instead was add a brief timer to my HOLD button that keeps the GO button enabled. User touches HOLD then GO. All good. Not exactly what I wanted but close enough to work for the user. Interestingly enough, I've now seen multiple other windoze tablet UIs that use the same approach, so I'm guessing I'm not the only one to run into this issue.