If you sheared the head off the oil drain bolt, the stem (the stud) of the bolt should still be stuck in the threads of the oil pan, not up inside it lying on the bottom. Once the head is broken off, the tension is removed from the bolt and you can usually 'walk' the stud out of a tapped hole by 'nudging' it in the correct direction to unscrew it. After a bit of the stud is sticking out, you can just grab it with a pair of pliers and work a lot faster. A small ***** punch as close to the edge of the bolt as you can get tends to work well; use the punch at about a 30 degree angle and tap it gently. You should see the bolt move slightly with every tap. Of course all of this is going to be more difficult working upside down, under a bike with limited room, and it may leak a bit of oil on you as you work. You could take the pan down, take out the screw and then reinstall the pan with a new gasket; which way is easier depends on you really.
That is a big bolt threaded into an aluminum pan so it is very possible that it damaged the threads in the pan before the head broke. If so, the pan will have to be repaired by using a larger plug in a newly tapped hole, or welded closed and re-drilled and tapped to original size, or something similar to make a permanent repair.
Brian
While torquing engine drain bolt to 25 Nm (30 Nm according manual) the bolt sheared off. It was a magnetic bolt, I think part of it is now lying in the oil pan. Has anybody already removed the oil pan and anything special I shoul pay attention to?