Originally Posted by KevinF

Would this race by any chance be the Mt. Washington Hill Climb?

I've gotten an Ultegra long-cage rear derailleur to shift into a 32-tooth MTB cassette. It isn't recommended, and it's not exactly quiet. You have to screw in the B-limit screw all the way to get the pulleys to clear, but it does work. I did it for the Mt. Washington Hill Climb; with a triple up front, I had a 30x32 low that I saved for the obscenely steep sections (i.e., 18%+).

One possibility is to scour E-Bay for an old MTB triple crankset / bottom-bracket combo. Strip the outer two chainrings off -- you sure won't be needing them on a 12% average grade. Keep your current front derailleur -- it can help keep the chain on. That would get you into the vicinity of a 24x27 low. You'll get smoother rear shifting, and you'll have some bailout gears should the weather be attrocious (assuming that this is Mt. Washington, it probably will be).