Start off doing an Idle.
When tossing the devilstick across from one handstick to the other, lift your
leg and have the devilstick roll over the top of your thigh. The devilstick
will do a half flip as it rolls over your leg before the other handstick
Practicing on doing it left to right and right to left. Once you can do it both ways it looks real nice when done solid. There are a couple of variations on doing it solid. One way is to never let the devilstick leave your leg. Just before it would roll off your leg you give it a push with the handstick, rolling it back the other way. The second is to let the devilstick actually roll off your leg, catch it with the handstick and then toss it back onto the leg for another roll over. They are subtle differences, but I have noticed with the first variation you can force the devilstick back and forth over the leg much quicker.
One thing to do as the devilstick is rolling over you leg is to do a Handstick Flip. Each time you roll the devilstick over your leg do a handstick flip with the handstick just used to do the rollover.