That is an Orange Crush thread, but I'll take a gander sometime. There are similar threads on the 640a specifically, did you see them? They are of course indexed, but noone has completed the project as I understand it. BigTwin put his method in the one thread, so any DIY fella with some skillz should be able to give it a go.
The best petcock protection appears to be the rallye skidplate boxes, which is a separate project. I suppose the best of both worlds would be to have CF/Kevlar tank guards and rallye skidplate boxes. My idea of complete protection. The 640a tank is damn tough, according to a few testimonies. Mine cracked, but it took a pickup truck broadsiding me to do that... The CF provides some structural rigidity to the guards and the Kevlar provides abrasion resistance; together they are supposedly a great combo and should augment the tank's inherent strength and may help out in quite a few situations. The rallye skidplate boxes will protect the petcock and the engine, perhaps your feet a bit as well.
Looking forward to your results.