My wife and I were doing the SG workout last night and I literally stumbled across a move I hadn't done since being on the drill team in high school. This is a basic variation of a very common move if you've ever seen a military drill team spinning rifles, and is in fact the basic rifle spinning move, only done extremely slow! I did it by accident while transitioning the hammer from one hand to another and immediately tried it out and it really burned my forearms!
Hold the shovelglove upright in front of you with your left hand (farther away from the head makes it much harder). Now SLOWLY rotate your left hand to the right to invert the shovelglove 180 degrees so it is now facing straight down. As the handle comes up in front of your face, switch hands and continue the rotation until the shovelglove is upright again.
That's one rep. Do X reps, then reverse for the other side.