This is an incredulously difficult
skateboarding trick which is employed in
flatland. If you are a good
flatland techer you will be able to conquer this one, though.
Start off in the regular nose manual position. Once you are in a very comfortable position, rotate so that your lead foot (left for regular, right for goofy) is longways over the nose, bend your other leg and get into a position as if balancing on one leg. Always keep your legs bent, or you will be kissing the concrete very quickly.
When you want to end the manual stretch your back foot back onto the board, then swivel so you are in your normal position once more. Push down and end the nose manual (unless you want to string a combo) and ride away satisfied that you have just accomplished a very hard trick.