A few All City Champs ago Sven from MPLS Does Bike made some home made triple coozies to give away at the race. I believe that it is made from foam tubes that are intended to be used as a water flotation toy, which were purchased at Ax-man a local kick ass surplus store.
This thing is incredibly useful. It keeps em cold and pads them so you don't have a bunch of cans digging into your back when you ride.
get one from Sven or make your own!