I use the same technique with the edge of a t-shirt (use one you don't mind getting cut up), as it seems to work the easiest for me. There's the crank, a plastic "o-ring", and the door panel. Try to work the edge of the shirt between the o-ring and the door panel.
Try to get the shirt somewhere past the 180* arc, and work it back and forth (in a sawing motion) a few times while working around the shaft. See if the crank comes off. If not, continue this motion and checking to see if the crank will come off. I usually work in 90* increments. After a little practice, you shouldn't ever have to do more than the full 360* around the window crank shaft before popping the clip off. BE CAREFUL to not loose that clip, it may or may not want to "spring" off.
When you out the window crank back on, it's quite easy (the reason for the design). Just put the clip back on the window crank, where the two V notiches (from clip) fit into the two slotted holes on the window crank. You should hear these V notches click into place when you put the crank back on. Don't forget to put the o-ring thing on first... ask me how I know

This guy uses the specialty tool, but should give you an idea of what you need to do:
You're basically trying to "catch" or "snag" one of the pieces of that clip and work it off the crank.