Using a program called Resource Hacker (link below) you can open the Luna Theme File (file/path below) and replace the bitmaps in it. Is there any chance that WinCustomize could endorse this as a way of skinning and host .msstyles skins?
http://rpi.net.au/~ajohnson/resourcehacker/
%SYSTEMROOT%\Resources\Themes\Luna\Luna.msstyles