RadialMenu now lets you remap the 2 buttons on the pen to Right Click and Middle Click. It also supports Hover Click, which is a must for artists. This mimics Wacom Pen button mapping and turn the SP3 into a Cintiq killer. I've already done some Mudbox sculpting and it's really great. I was able to sculpt while on the subway without the need for a keyboard.
http://radialmenu.weebly.com/
http://radialmenu.weebly.com/