Yes, that's what I'm thinking of doing. As my back panel is aluminium I was planning to use a thin piece of billet which would be easy to work with to radius the edges and cut the hole for the filler cap, then maybe paint it to same colour as the car. There are plenty of authentic looking flip-up filler caps in polished aluminium and I can put in a new extended filler pipe. It should be quite simple except for shaping the plate in which the fuel filler cap will be bolted. When I do it I will post pics, but probably won't have time until the end of January. If you don't feel skilled enough to shape the piece of stainless, you could ask a machine shop to do it for you.
