I think they do this on the made up 'Eleanors', i've seen a rubber hose from the fender cap to a snake of piping down to the top of the tank inlet and a rubber hose to connect those 2. I imagine you either have to have piping bent in a machine or be able to weld pipes together.
Jon
If you have a coupe, I don't think there is really room for it to fit there. The only cars I have seen with gas caps like that were fastbacks. Personally, I think that the original gas cap location is awesome and wouldn't change it.
depending on the amount of work you are willing to do, you can move the gas filler opening anywhere you want. if you want you can even put it on the front fender. personally i am with tx65coupe, the stock location is the best place.