In addition to Martin's innovative idea to use sticky food wrap to cover up the cowl and wipers (that I didn't actually get a good photo of), he decided to try to make an aerodynamic "trip wire" as he called it that is featured on the Volt, like this:
The point was to make a little dip just before that extreme edge the air has to deal with to add an effect similar to the effect of dimples in a golf ball...it just wasn't as pretty as it is in the Volt.