I have found (once you manage to drill out the snapped bolt, and re-thread the hole) that if you put the puller on, and ad tension (not too much, just get the pressure on) then soak with WD-40 or Penetrene as Emmo mentioned, it should slowly come free using both Grumpy s method, and a suitable tire lever or long Flathead screw driver.
I.E.
WD-40, Wait, Apply Pressure, WD-40, Wait, Slightly up pressure, Insert lever under lip of flywheel, Slowly work your way around the flywheel, in 1cm steps, lighly tapping the lever with a hammer each time, WD-40, Wait, Bump puller, then go areound with the lever again, upping the pressure slightly each new lap.
