Arguably, there are enough people walking around with stones in their shoes that altering your movement with that method would be masking enough - until they're able to simulate how you're normal gait would change with x sized stone at whatever location in your shoe..

Alternatively, I've heard (don't have the source handy) that they're looking at other stuff that the stone in shoe might not change such as overall height and knee to leg to hip to foot stature and angular momentum ratios. Who knows?