How can I shed more pounds quickly for marathon?

I am currently training for a marathon. It's not until November, so I am slowly racking up the mileage. What I want to know is how can I lose about 10 to 20 more pounds so I can shave off a little time? I am by no mean fat. I have an athletic build, but I just want to shrink down, so I can get a better time. Any suggestions?|||Lay off the twinkies lard ***