Don't magnets slide apart use less force then the force holding them together, is the same true for opposing magnets? Can opposing magnets be slid into place with less force then the force pushing them apart to power a human powered vehicle?
I see what you are driving at. Try experimenting with shielding materials.
If you dismantle an old scrapped computer hard drive, you will find powerful magnets attached to some mumetal shielding underneath the coil that moves around. This might be a good starting point.