If you really need brakes in the up position there are some units on the market, specifically for cykelcross. They are small levers that tap into the brake cable and work by effectively shortening the cable housing.
My husband's Specialized came with similar and he claims to never use them, so we were talking about hauling both bikes down to the LBS this weekend and having them swapped over to mine. I'm thinkin' it's an excellent idea.