I've done it. The shape of the shadow isn't perfect, you could try to improve on it by your own. You'd have to edit the alpha channel, which looks like a grey-scaled something. Anything that is black on the alpha channel, will be transparent. The lighter an area gets, the more opaque it is. I didn't try the modell in-game, but since I just removed the docks, there should be no serious bugs. Maybe the shadow flies around or the building stands to deep in the ground. You could improve on this using nifskope. It's pretty much forward. Select the part you want to edit, right click at it and pick transform. Increase the value at z to move the object up- or downwards.
There's one major problem, though: the building has no ground level. If it stands on a hill, you'll see a gap here and there, this ways. A simple way to fix this, is mirror the whole building and move the mirrored copy downwards, but that's ugly and won't work at the stairs. There's a more professional way, but I'd have to texture the additional faces and I hate texturing. Maybe I come back to this some day...