Know naught re drilling the balls, but wrt magnetic 'support' – that ain't easy..esp with plain permanent magnets and no feedback control. The ball needs to be perfectly in the centre of the magnetic field. IF you ever get it into that spot, a slight breeze will push it off and the closest magnet will pull it in. Any MINUTE movement of the sculpture/ball will do the same, even the vibration of passing feet on a concrete floor!
Spinning the ball helps a little…
There are electronic ways of doing it with two permmagnets and a solenoid, with optical position feedback, etc, but hard to hide in your creation..Also, if the ball is not a magnet, the magnetic force needs to pull from the top to oppose gravity, so even harder to hide the magnets/solenoid.
google magnetic levitation – lots of stuff.
Joe