Unfortunately the fix they suggest there is exactly the one I'm having trouble implementing.
For some reason, the SetImportedTerrainOffset cheat doesn't work for me.
Update: Found a fix! ConstrainFloorElevation false cheat, followed by a flattening of the terrain, followed by sledgehammering all objects in the house, then hitting undo on that sledgehamering. After flattening, the walls and such will all be fixed, but all the objects, including windows, doors and roof, will be floating where they were before. Side note: This doesn't seem to effect a basement; if you've got a basement, best to delete it before trying any of this.