Wear different pieces of different costumes all over.
Wear half your hair up and half down. Different shoes, make the difference striking (tennis shoe or work boot on one foot, high heeled red pump on the other).
I wore flannel shirt, tutu, bib overalls with one side hooked and other not, tiara and a goofy hat, etc. Put sign on your back that says "couldn't decide!"
This won most original at my hometown community contest.
Thanks to Cindy in IL for this fun idea!