Not that I know of...book now, keep watching the rates, and if they go down then call and they'll adjust the price. I've already done that 2x in about 6 weeks for my first trip in March '09!
(that being said, if EVERYbody books now, then there'd be no reaso for them to lower the prices later, so I guess you could argue that booking now would decrease the chance of a discount later!
But, budget the price as it stands today, and if it HAPPENS to go down, then consider it a bonus.