Yeah, I've had the same problem max-a-mil's had (but I was just running the entire cassette) with the chain jumping the cog in the past. Now I've got a SS bike that I just tightened the limiting screws on the derailleurs until they don't move anymore.

but that's still really awesome... I see the two masterlinks there to make the chain shortening easier... I was thinking about doing that with a single fixed cog in the rear and two chainrings up front, one for high headwinds and things like bicycle polo, and the other for going fast with a tailwind and such... but that's taken that idea times 2!