Realizing this probably won't work but that it'd be fun to build and try (I was right :-)), I built a permanent magnet motor based much on a water wheel. The idea was to have magnets on the periphery of a wheel, with the magnets arranged such that a push force on them would impart torque on the center of the wheel.
Even though this didn't work, it illustrates a useful trick you can do with steel to shape the magnetic field.
A problem is that as the magnets repel, at some point they get stuck. In this case it's because of additional repulsion encountered with one of the magnets that stick out far enough. See the following animation.
To fix the above problem a keeper can be used. A keeper is a piece of metal that is often used with horseshoe magnets to help them keep their magnetic properties longer. The keeper is put across the ends of the horseshoe magnet so that the field will go from the north of the magnet, and through the keeper instead of through the air, to the south of the magnet. In this case I am using the keeper more for shaping the field so I should call it a shaper.
Unfortunately, I added a third set of shapers on the next set of magnets but the wheel would not go past them. The potential energy present before releasing the wheel to start it turning, which turned into kinetic energy in order to add a little extra to the repelling forces was not enough to make it go farther. The magnets themselves did not introduce any new energy.