I'm not certain what you mean by the parcel shelf area. The space layout (profile view) looks something like this (not proportionate):
windshield
/ 1 2 3
/ front seats back seats convertible mechanism trunk
|__________| ___________|____________________|___________|

Areas 1 2 3 signify the three "open" areas in the car. Areas 1 and 2 are loosely connected, there's room for air to move from 1 and 2. However, the trunk is pretty much sealed off from the back.

It seems to me a free air setup might work here... Since one of the requirements is to have a baffle seal off the back from the front...

Calvin