No, I think that the bendy handle design is your best bet. If you follow a growth ring and there are no bad knots I would not back it with rawhide. You can pull osage further than 50% of its length, but you're likely to induce set. Sinew is the only backing I can think of that might do what you want and I would also flip the tips while I was at it. It's a lot easier to make a longer bow though...
George