Backface culling and normal inverting

This would be useful for making 3D gizmos like this:

Because it draws in order there's no way for me to hide the shadow effect from showing underneath. If I could make the cone's inside (uncapped) not draw its backfaces I could make the cone draw before the shadow, or alternately I could just make the disc not draw its backface.

With the culling it'd also be useful to flip the geometry normals, this would make stuff like cel-shading a little more straightforward/intuitive than making sure to draw it first.