If you "seed" the tank, you can add a small amount of fish to keep up the ammonia source. Seeding allows you to re-establish a new filter without having to go fishless.
Plants can also be added, since the filter will begin to function as a normally estabished filter. You may have at worst a "mini-cycle", which will only occur if you add too many or not enough fish. For a 55, I would get a least 6 tetras or an equal amount of fish of that size.