Try this. Unscrew the spindle bolt until the head protrudes above the surface of the crankarm slightly. If you can find a bolt that is slightly longer so that you can screw it all the way in and still have the bolt head protrude past the crankarm this would be better. Now holding the bike up by the crankarm with the bike parallel to the floor hit the head of the bolt with a soft head hammer or mallet. Don't get too carried away with the hammering, you don't want to ruin the bolt or the spindle threads. Also right before attempting this pour some boiling water over the crank. Of course it's much easier if you have someone to hold the crankarm while you do the hammering but can be done solo if you're strong enough.