If you look at Wall3D class, you'll see that the method createWallGeometries is used to create the main parts of a wall and also to create baseboards as if they were some small walls. Maybe you could inspire yourself of the same system for a cornice, except that you will have to manage a profile in createVerticalPartGeometry method instead of a simple vertical plan which makes it more difficult.
Round walls are actually a serial of small vertical parts and you should create a getWallCornicePoints that will return the global shape of the cornice along the wall like getWallBaseboardPoints does.