^^ to be optimized, yes. but it would work to some degree if you had a garden hose piping about under the carpet... though it wouldn't be noticeable/significant.
I was thinking a tube (cylinder) around 4-6" in diameter, snaked through, but kept as straight as practical, though it could be a "flat" tube or anything else that reduced the pressure differential enough to have a significant effect (though I haven't done any calculations on what would constitute a significant effect). It should kill two birds with one stone- both reducing the air force pushing the car back, and lowering the pull effect of the low pressure area behind the car, whereas boat tails (for example) basically only affect the back (or dams, the front).
I'm going to read up on the link you posted frank, thanks.
to clarify: I said center line because I assumed the peak (high/low) barometric pressure values would be approx in that area. The main idea is to connect the peak high to peak low, wherever they may be (well... for the most part).
My main concern in the whole idea (atm) is that by effectively reducing the size of the cab), the importance of flow around the outside of the vehicle (outside drag) will be reduced (assuming the idea works as I imagine it, anyway). So, if aero mods on the outside of the vehicle reduced drag by 15%, and a duct is then added that increases efficiency, it then would reduce the gains of the outside mods, (dunno how much... but that's the crux of it).
Anyone have access to a miniature wind tunnel? I used to use them all the time for modifying aerodynamics of racing vehicles I designed back in high school... but they were always on loan from other schools, so I doubt they would have one there now.