Unless I'm mistaken, I believe a pinwheel is a Stall Turn/Hammerhead type maneuver that goes past the normal 180 degrees. Your description of "plane pitches up" has me a bit confused. Do you mean a vertical up line, or a sudden pitch up? There is also a maneuver called a windmill that involves a plane pitching up (basically a tight inside loop) but it doesn't involve a stall turn.

As for the pinwheel... I suppose you can enter this from anytime you are pointed up, i.e. torque roll, vertical line, etc. To start, fly good clean vertical line. You need to be sure it is really veritcal. Slow down like you are getting ready to do a stall turn. Then do the stall turn but don't release rudder across the top. Instead hold full ruder and add power to do the 360 stall turn. Engine torque and outside wing generating more lift than inside wing will cause all sorts of funnies. You may have to play aileron and elevator to keep the plane vertical during the pinwheel. Sometimes it also helps to kick a little opposite rudder just before the pinwheel so that you have a bit more yaw momentum before the maneuver. I suppose one could just thrust vector the whole thing but this maneuver seems easier on larger planes where inertia is in your favor.

Cheers