Under arm DS mess:
Rather than crossing your arms "over" for the backhand hits, cross your arm "under" for the hit.
Here's a video of windmills, mills mess, and underarm mills mess:
Behind the back DS mess:
Rather than crossing your arms over for the backhand hit, put your arm behind your back for each backhand hit.
Under the leg DS mess:
Rather than crossing your arms over for the backhand hit, put your arm under your leg for each backhand hit.
Flourished DS mess:
When crossing your arms over for the backhand hit, do a baton flourish or thumb roll flourish before each backhand hit.
I first came across this trick on Seth Golub's devilstick page. It is Mills Mess but while doing a helicopter. You can check out his description if you'd like.
The Barrage mess:
When I started showing this trick to people they said that it looked similar to the three ball trick Burke's Barrage. However, I have since come up with a trick below that better mimics Burke's Barrage moves, and have renamed this to the Barrage Mess.
When you start to cross one arm over another turn your handstick around so that the backhand hit will be done with the back side of the handstick. So when the hit is done to reverse the direction of the devilstick, the hand is in the following position: knuckles will be up with the front side of the handstick pointing at you, and the back side of the handstick is doing the hit.
When you first start to work on this trick you will need to slow it down. Turning the handsticks around for the back side hits can get pretty fast and you will need to have control for stopping the devilstick and reversing the direction. It takes awhile to get used to hitting a devilstick in this position.