you can also invert the selection after you've done the extrudeand then Shift+Alt click on the Layer Palette's thumbnail and that will switch the selection to the extruded edge only - you can dodge and burn some shadows and highlights or smooth out some of those lines by locking the layer's transparency and using a Guassian Blur.
(
maiden is filmed before a live studio audience,
Wed 6 May 2009, 18:48,
archived)