Hi Martyn,
Not wanting to question your post, but are you sure you have Magteks? (Not saying you can't read or don't have an SP, of course - just asking!!) :)
If so, then even though there is only a small Mg content in them, the wheels do have a special primer applied to inhibit oxidization, different to that used on the standard Enkie type wheels.
Also, the paint applied to the Magteks is very thin, so you should be able to get away with lightly "keying" the surface (with say, "Scothbrite") rather than sand-blasting it.
If you do indeed have Magteks, then I would personally take them to a specialist shop, but if you have the standard pattern wheel, you can pretty much do what you like to them - pain, powdercoat, stove enamel.
Andy.
NSR-WORLD.COM