I think you're out of luck there. The RC is about 500 builds away from the final version (7100 vs 7600), and to my knowledge MS have stated that their won't be an in-place upgrade from RC to final. You can't even do that with RTM, which is essentially the same software as final.
As tempting as it was to make the RC my primary OS, I stuck with a dual-boot for precisely this reason. It really is a try-before-you-buy option.