I suppose something could be designed and built so that it bolts on where the fuel filler is (using a gasket/seal to join the two, of course), and sits on top of the stock tank like a hard-sided tank bag for two or three extra gallons. You could even shape and pad the back of it to give you something comfortable to lean on while you go those extra miles.
Or perhaps a hollow plastic dummy shaped like a passenger that sits behind you. Plumb a hose from the dummy's, uh, "lower regions" through a pump to your tank. Fill the dummy up with gasoline (through the filler in the top of its head) and you're 2-up for the long haul! When you're low on fuel, just pump some out of the dummy. Thank you, Gas Buddy!
Or maybe a hollow harpoon attached to a pump. Just find some truck or SUV where the driver is immersed in an all-important cellphone conversation, roll up behind, puncture their tank, and suck their fuel into your bike! It's in-flight refueling for bikes!
Or perhaps the solution is to burn less gas. You could fab-and-fit a special set of intake manifolds on two of your cylinders that, when a switch is thrown, pull air from a separate filter instead of through the carbs. With just the flip of a switch, you'll be riding a frugal twin instead of a thirsty literbike!
-Swan (who dropped out of college when he found out there was no degree offered in the field of Mad Science)
