A reviewer/endorser on Fixed Gear gallery wrote that a chemist had determined that Pro Link chain lube is just mineral spirits and synthetic motor oil. I don't know that I believe that, but it got me thinking.
I'm going to try using sugar water on my chain. The ants eating the sugar will remove dirt from the chain. The movement of the drive train will crush the ants, allowing the juices of their bodies to lubricate it. Regular applications of sugar water will keep a steady supply of ants coming. They will also no doubt appreciate the nutrients provided by the crushed bodies of their predecessors.
It's 100 per cent biodegradable and renewable, but I guess it isn't cruelty free.