Is it cheating to bend the film plane? If you cut a piece of 6" PVC in half and put an 8x10 sheet against the curved side, you'd have a 3" focal length, and I think that's pretty wide for 8x10 - 75mm, I think that's the equivalent of 11mm on a 35mm. Pretty sure that'l get you close to 180 degrees coverage.
That's basically what I did w/ the coffee can pinhole. It was made with the smaller cans, not the big Folger's type cans, but the smaller ones that only hold about 12-14 oz of beans.