Nice one, bagginsbill! As I mentioned earlier I imagine one could forego the use of an image map altogether and achieve results similar to OP's original intent with a combination of 3D texture nodes. This would avoid any seam problems and various issues with redistribution of images. Of course alpha masks would be needed to exclude brows, etc. Along these lines of thought, if OP did indeed intend to share the results it would simply be a matter of an .mc6 with an empty image map node plugged into relevant surfaces for the end user to apply whatever textures into the mix... anyway, just thinking out loud.