It's easy. All you need to do is rotate (yaw) your hand when flipping so that the coin spins but never actually flips, or a little slower so it flips only once.

It's easy. All you need to do is rotate (yaw) your hand when flipping so that the coin spins but never actually flips, or a little slower so it flips only once. A watchful eye can detect it happening, though. You can preview the effect by spinning a coin slowly on a table. This is a common problem in intro Physics Mechanics class.