I don't know of a way other than disassembling the freewheel. Use a strong drift punch or a junk screwdriver whose tip can fit into the two holes. You need to work clockwise, as it is a reverse/left-hand thread. A few whacks on each hole should loosen it so that you can remove the top piece. Make sure you have something underneath to catch the tiny ball bearings. Take out the pawls and springs and then clamp the remainder of the derailleur body in a vise, grab the rim and turn counter-clockwise.