Right heres what i did.

Get a couple of G clamps and an inch thick (at most) longish block of wood, a touch wider than the pulley.

Pop the bolt back into the crank a few turns & place a block of wood over the end of the bolt, take your g clamps and wind them down so that they just fit over the blocks of wood and the threaded part you turn touches the pulley, one on the front of the engine one on the back, then slowly wind the G clamps in.

I found this was nice and cheap as had the bits lying around the garage and was nice and compact.