A "short magnetic pulse" is essentially an electromagnetic wave, or in other terms, a burst of photons. Electromagnetic waves/photons would not be repelled by the second electromagnet. Again, unless some of those photons produced escape the platform in a non-symmetric way, you get no net motion of the platform. If more escape in one direction than the other, you have a photon rocket again.
You simply cannot "fool" the universe into violating the conservation of momentum, no matter what "tricks" you try to use. As you make your schemes more and more complex all you are doing is making it more likely that you will lose track of all the momentum transfers along the way, something nature never does.