not as easy as a good rap
but
something like this might be what you are looking for
gascapmod Photo Gallery by fred harmon at pbase.com
Interesting. There is a lot of key work to gas up, especially if you keep fuel records in a notebook in your luggage. Remove key from ignition, open gas cap, remove key, add gas, reinsert key to close cap, remove, open luggage, remove key, turn on ignition, record gas//mileage, remove key, open luggage to return notebook (I never remove the key from unlocked luggage after I once took a nice, long ride with the side case lid flapping in the breeze), lock luggage, reinsert key in ignition. Yikes, it sounds even worse than it is. Not sure if it's worth the trouble of the mod, but that is a nice option should the task become too onerous someday. Still, I think I'll reserve rapping for my musical career.