If you're handy in making your terrain as a model, which you could make to fit exactly to your 'parts', you could import it and derive a heightmap from that, then displace the terrain from that heightmap (ortho render with luminosity and an altitude fuzzy zone), and add procedural detail to give it spunk.
Another idea would be to place a number of displacable cubes around and behind you parts, more or less fitting, and add displacement and texture to those. Plus is that you can place those cubes very precisely, and with one set of shaders attached to all, they kind of merge into eachother as one 'wall of stone'.