Maybe you can export the heightmap, import it in WorldMachine and then export the resulting terrain as a model, import it in a 3d program, maybe edit it so it isn't a sheet but has a cube over or under it, for collision's sake, export it again as a model UE1 can read and finally import the model into UE1 and place it as a brush.
Won't get you layers though. Perhaps you can get those using masked combiners that combine tiny TexScalers of the terrain textures with the layer's alpha maps as masks, and then you stretch out the combiner over the whole terrain?
As he said, the principles are different so there is no way to easily convert them. If you get any results out of this it would be cool if you post them here. Just for curiosity's sake.