How to make a creeper cannon in minercaft 1.7.4 (or any version i guess haven't tried yet in 1.7.10) NO REDSTONE!!!!!

1.as you can see you'll need to build a 4 block high floating watch tower structure

2.then spawn a creeper right click it with a flint and steel

3.then you'll need to punch him with an item with knockback 2 item while he's fusing

THERE WE GO YOUR CREEPER CANNON NO REDSTONE AT ALL :D