Maybe one of the better informed guys on here can teach both of us a better way, but here is how I do it. Doesn't make sense to buy a special tool for a one time use if there even is such a tool.
Make a hook out of a small screwdriver and fish the clip off of the crank from the orientation of the crank arm. You will probably distort the clip, but you can reshape it once off, or just buy new ones from Dennis Carpenter.
Once the crank is off, hack saw the clip grooves on the back side of the crank to extend it all the way opposite of the arm (Be careful not to score the under side of the crank. Protect with a piece of sheet metal, or just be real careful). This will facilitate future removal with a tool you can easily make from another piece of sheet metal. Just a slot wide enough to slip into the grooves in the boss, but contact the clip and push it off of the crank boss. Then bend a 90 degree bend about 4 inches away form the slot to use as a sort of handle to push on.
Wish I could draw a picture on here, but good luck. The secret is a little persistence.