Its not easy to tell from the pix but how much room is there underneath the pulley???

enough to get a head of a ground down HT bolt???
perhaps an M6 which could sit between the teeth in the recess keeping it close to the pulley body.

Just wondering if you could grind the heads to make them fit into the available space, then with them screwed into some steel with a central bolt, it may be enough to prise it off.....

but only if there's enough room.