Broken crankshaft pulley bolt on

The only possibility I can suggest is that which is called and 'Easyout.' These are available at parts stores and come (normally) with a sized drill and a special bit with left-hand threads.
First a hole is drilled with the provided drill bit, then the removal bit is screwed into the new hole and turned counter-clockwise which further inserts the removal bit and, if the removal bit does not snap, the broken threaded shank should back out.
I would suggest soaking the broken part with penetrating lubricant first and allowing it time to seep into the threads of the broken bolt.