The plugged grille :
Notice the creased edges on the tail end :
Hyundai Reveals 2011 Sonata Hybrid, gets 39mpg Highway, can Reach Speeds of up to 62mph in Electric Mode - Carscoop
More aero wheels :
Large portion of the grille is blocked ( look behind the slats as well )
One of the main things that was mentioned in reducing the Cd was the back end of the car. Notice the stock rear has a more curved bumper at the corners :
Versus the hybrids sharp cut off ( much like that seen on the Prius )
On closer inspection ..... look at all that crap hanging down under the chassis in that last image !!