The first thing the cheat does in this move is to place the dice in the cup so they are squarely stacked on top of each other and so that they are resting tight against the inside wall of the dice cup.  The cheat then rotates the vertically held cup in a circular motion (see diagram).  This motion keeps the dice's orientation and position fixed by creating a centrifugal force that keeps the stacked dice tight against the inner wall of the dice cup but spinning around the circular interior.