Or, the stylus could act like a WiiMote with its own accelerometer, and relay the information to the iPad with Bluetooth, but hey, lets not think outside of the box.
Cool idea, unfortunately, that would required a powered pen and you would not be able to draw a sketch while skydiving. I could deal with changing batteries in my pen, Not being able to draw a picture after jumping out of an aircraft would be a deal breaker for me.