I'm not sure that the solution offered by Michal is far from what you are looking for! As far as I can see, he's using the same surface, plugged into different generators within the same RC object. The only thing that is different is the clipping splines that are applied to the areas that have common edges. The way I look at it is that the areas should be looked at in plan. If the edges of any areas are in the same place, i.e. there are two edges, one under the other, in plan, then you need to make another area with a clipping shape.
In the end you should have a single surface, multiple shapes which define the different levels, and one railclone. For each level, you need a new generator with the surface and the specific area plugged in as Michal showed.
Perhaps that was helpful... perhaps not. I hope so.