Step 6: Add Battery and Switch
I hollowed this space out with the pen knife. The Dremel tool works, but it takes longer. You also need to keep the new hole space snug to the battery. This is because the battery is not held in with anything but the elasticity of foam, so don't go over board with the knife.
Then solder the + from the battery clip to one of the connections on the switch. Next solder a wire to a different connection. In other words, solder it so it works as a switch.
You will want extensions on the wires so they reach all the way to the front LED assemblies.