There's really no easy way to handle a 40-foot extension ladder by yourself. The U-Teck Rung Runner is a two-wheeled dolly designed specifically for moving ladders of any size. The ladder is held on by a strap; since it's supported from the middle, the weight you have to lift is greatly reduced. The two wheels can pivot on a dime and have large pneumatic tires that can handle rough terrain. Using this dolly should put a lot less strain on your back than carrying ladders by hand. Now you just need a tool to foot the ladder for you.
Price: $80. 800-542-7011. uteck.com.