I'm guessing "slantback" might be out of the question. I saw this snugtop version a few months ago and these are just a few examples of what came up when I Googled it. I have a crappy internet connection and some of the other links wouldn't come up.
The way these guys are doing it I don't think the areo benefits are as good and sadly I've only seen this particular thing for the Hummer 3 which isn't even close to being smooth in the first place.
Snugtop - Custom Fiberglass Manufacturing, Truck Cap & Tonneau Top Covers, Camper Shells Tops, Customized Truck Toppers, Pick Up Truck Canopy
SNUGTOP SLANT BACK BED COVER / 2009 HUMMER H3T
First Look - H3T Slantback Shell - Pirate4x4.Com Bulletin Board