Put tires over the flagpole.

Get 40-50 used tires, rent a cherrypicker (get the class together and collect the cash), connect a pulley system to the cherrypicker, make sure the person in the cherrypicker is safely tied in, pull up to the flagpole at night and use people at the base to work the pulleys to raise the tires, the person in the basket slides them over the top.

If you are good you'll paint the tires and line them up so they spell Class of 05

ichi

ps I deny any involvement in your endeavor or any similar endeavors that may or may not have taken place at my high school