A Current Affair tonight, page-104

I'm aware of all that but you should realize that the magnetic particles that you hope will be propelled nicely in the direction intended by the diamagnetic force are also subject to all the other forces of physics. It is not a pure laboratory case of magnetism only. So the skin is a physical barrier which I suggest is much greater than the force.
PS Do you think quantum tunneling might be involved? That has very low probability.