Found the Hucho reference (4.4.4 in Aerodynamics of Road Vehicles), and he's certainly cautious when approaching the problem (raising the roof & frontal area to decrease Cd). Essentially he says what we have: it's technically possible, but not without experimentation to ensure the additional A doesn't outweigh the decreased Cd.
That supports my advice that it would be risky to just "guess" at this and build something permanent.
EDIT: he says essentially the same thing about increasing side camber (and A) as a means for reducing Cd, in 4.4.6.
FYI, there's already a decent thread on the issues in this particular debate, so I'll stop commenting about it now.
http://ecomodder.com/forum/showthrea...bad-20460.html