The main connection occurs where the eyes enter the eye sockets. There is a small protrusion on the inside of the eyes which clips into a relief point near where the nose sternum would be. The purpose of creating the aforementioned tools is to overcome this grip point with force thereby separating the two pieces. As luck would have it, the space between the head and the brain stalk is smooth on both pieces. This would allow you to insert a thin object between them and apply force.
So grab your switchblade (or have your mom supervise you with a butter knife). Insert the blade end up between the head and brain. Gently twist the knife so that the top edge is pushing against the brain. Don't worry, you won't actually get far enough to cut the brain. Oh wait, it popped off already? Dang, that was easy.
Congratulations! Bionicle lobotomy! See the video here.