Yes, a radiant barrier would work, however, I would use aluminized polyester (space blanket) instead of foil. In my humble opinion, I would abandon the idea alltogether. To much work for something that will rip off in a short amount of time. (not to mention looking like crap)
Instead...Insulate, Insulate, Insulate. Payback in all seasons.
You could also go with the radiant barrier idea in the attic by stapling alum. poly. to your rafters (assuming it is a stick built with enough room to work).
An attic fan as previously mentioned would do wonders. I am also going this route as soon at it warms up. They make solar powered ones, so no wiring, and feels good putting up pv.
Better yet, go to
www.builditsolar.com This is one of the absolute best sites on the internet. I visit it just about daily and have implimented several projects listed there. Tons of info, ideas, DIY, FREE. >Check it out.