Heat the balancer around the center hole to make the hole bigger, you get an easier fit that way. Use a handheld propane torch or something but don't heat too much or you may compromise the bond of the rubber membrane in between the hub and the pulley (unless you have a solid metal balancer, I dunno). By getting it just hot enough that you don't want to touch it with bare hands, would help a lot.
Your trick would also work but it still sends shocks through the length of the crank. Maybe try both these tricks together and be gentle. I'm facing the same challenge again soon with mine, and I also need a new balancer... just noticed a crack on mine where the keyway is. Didn't see it when I took it off. Didn't look for one either.
If you drill and tap, you need to get the drill hole perfectly straight with the crank. If you screw it up, well, you are no worse off than what you started with - no tapped hole at the end of the crank
