Once you get the front 3 set and mounted, instead of adding an air dam, could you pack something underneath the leading edge to act as an air dam? Might be easier than adding a piece of plastic or something and trying to create a continuous surface between the front of the panels and top edge of the roof. I think it would accomplish the same result. If you're concerned about wind/air flow getting under the panels.
Have you considered using low profile flex panels which could be mounted nearly flush to the roof's surface? They're usually pretty thin, and a dab of sealant all around them would solve the air dam issue.
