If you insert a heated allen wrench into the screw socket, you will get more effective heating of the screw because the allen wrench has more surface contact than either a rod or a soldering tip.

Another more aggressive alternative would be to chuck a section of allen wrench into a low-torque impact driver (such as a 12V cordless tool from Dewalt or Makita or Milwaukee) and try to back the screws out. Be sure you have a good fit between the wrench and the socket.