From the saw position. When the devilstick rolls off of the left handstick and lands on the right handstick you will need to move your left arm toward the center of your body. As the devilstick rolls over the front side of the right handstick you want to then bring the devilstick around and under your arm, so it will roll over the back side of the left handstick. After it rolls over the back side of the left handstick bring the right handstick over to catch the devilstick on the front side of the handstick. Then, roll the devilstick over the front side of the left handstick. That's one half of the trick. You can then do the same move on the back side of the right handstick. The devilstick will be doing a "figure 8" around your arms.
Having the devilstick hit your arm as it spins is the biggest obstacle to overcome. To make thing a little easier, try to keep your arm straight and lean your body to the right when rolling the devilstick to the outside, onto the back side, of the left handstick, and vise versa.
Walter Park showed me for some people it is much easier to do this trick if you are doing a reverse saw. When doing a reverse saw you do not have to try to get the devilstick to go underneath your arm. You just need to make sure that the devilstick is far enough on the outside of your arm so that it will not run into the top of your forearm.