hmmmm other ideas......
Wear sun glasses and tell the Scool Overseer that you are prepared to give your talk, however you just got back from an eye exam and your pupels are dialated and you won't be able to read without your shades.
Wear your old converse tennis shoes and tell the SO that you are prepared to give the talk but could not find your dress shoes, if he offers to loan you a pair, make sure that you tell him about your bad case of athletes foot.