I haven't bothered yet, since all my routes up to 5 hours pass convenience stores at some point or another, but I've thought of carrying a squeeze bottle of chocolate sauce. I'd take a bottle that's partly or mostly empty, for obvious weight reasons. Not particularly sophisticated as sports gels go, but I don't believe that careful balancing of various forms of carbohydrates, etc., would make a perceptible difference; taking in some calories, any calories, has alway seemed to work for me. But then my mid-ride refreshment, other than the water I carry, usually consists of a Reese's Fast Break candy bar and a diet Pepsi. Delicious.