Check it out -- bike hacker Bruce Ingle created a two chain fixed gear bike from leftovers, spare parts, and aftermarket modifications.
Of this bike, Sheldon Brown writes, "Disclaimer: This is a highly-advanced hack! Do not attempt it unless you have great confidence in your metalworking and mechanical ability. This article assumes that you are already very familiar with the inner workings of Sturmey-Archer AW 3-speed hubs. If you have any questions that you can't figure out the answer to from this article, you're not ready for this!"
@Hipster - Sheldon passed away two years ago, so I'm fairly certain your postscript won't reach his ears. I'd be interested in posting the details of your brother's dual chain bike with the two speed hub.