Thats starting to sound like the "blown flaps" the tsr-2 had. They made the airflow stick to the flaps during landing and take off and provide massive lift. In our case, it would make the airflow stick to the body and with a suitable body shape, reduce the wake.
If you are thinking of using it to fill the wake from the rear view mirrors, first remove the mirrors and see what mpg gains you get. If you get something then go ahead with the wake filling idea, otherwise don't bother!
I believe renault are doing some research on "synthetic jets" but are using piezo type jobbies in slots around the tail of the car to make the airflow stick to the body.
Heres a link to an article on it:
Green Car Congress: Renault Altica: 44MPG Diesel Concept with Active Airflow Management
Renault Altica : News & Reports : Motoring : Web Wombat
http://www.jafmonline.net/modules/ht...-022069-A4.pdf
That last link appears to mention reducing drag by creating your own wake.......familiar?
ollie