Most Helpful Guy
Don't go on heels or buy him a shoes with a thick or bigger sole ( Don't know the spelling )
Most Helpful Girl
If you're so concerned about it, why not get a nice pair of flat pumps?
However, during your formal I doubt you're going to be overly concerned that you're taller, why pay any attention to minute details that will take away the joy of the entire evening?
No one else is going to notice/care, so why should you let it bother you?