If you do not often remove or lower the seat, you can replace the seatpost skewer with a bolt and nut. Your LBS should have just the right ones, or you could take the skewer to a hardware store and match it up. (Don't waste time at a mega-builder-supply store, go to an old fashioned nut & bolt hardware store.)

I did this with my Trek "rainbike," after the skewer rusted and broke. This mod will shave a few grams of useless weight from your bike, as well.