Since it's in a pretty significant magnetic field, I'm wondering if a coil, of very thin wire, placed off center would work. The magentic field (which is changing pretty often, switching to maintain the suspension) passing through the coil would induce a current and that current flow produces it's own field. That offcenter, small field should impart a force, which being unequal (off center) would cause the ball to spin.
I'm just shooting in the dark for this one.. but is there a reason it won't work? Seems easy enough to try if you are experimenting anyway..
The only problem I can think of is that the force may be either to small to have any real effect, or too large, and cause it to spin much too fast.
Kind of an air-bearinged induction motor?