Here is what I would try: (1,0,0) (1,0,0) (1,0,0) (0,0,1) (0,0,1) (0,0,1) (0,0,1) (0,0,0) (0,0,0)
Why? Others picked up on the sphere indicating a 3-dimentional answer. I looked at the keys as a direction, instead of a point. When you add them all up, you get a point that is (5,8,4). So the additional keys will bring the point to (8,8,8) – a perfect cube. Additionally, I added two points at the end so that the total number of keys pressed is 25 (5x5), the witch gave us the first 16 (4x4).