Here's something else you can do to shorten up the amount of mainsheet you need; hang your top blocks from a longer tail or leash or strap or something, off the boom. Every inch you can lower the blocks saves 9" of sheet on a 9-1 main set up.

I have added a Dyneema rock climbing strap, about 12" long, to the top of my blocks, that I then pass through the clew, around the boom and back down to the S hook I have shackled to my top blocks. This lowers the top blocks about 4" total from the boom, and has the added benefit of being able to quickly unhook the blocks from the boom when I get to the beach. No tools required, I just slip the end of the loop off the S hook.