Check out Jettengineering.com, Dub Jett makes several tanks with silicone bladders that take the nitro fine. They also allow muffler pressure, and you set your carb the same as usual. The bladder resides inside a polyethylene tank, and the muffler pressure is fed into the poly tank. They're made for pylon racing, to give a good needle the whole flight, and avoid the lean runs or lean period at the end.
I've been thinking about condoms or balloons to make my own, but the silicone bladder beats them all hands down.
-Tom