The idea is quite clever, but not new. In fact, it has certain application:
https://en.wikipedia.org/wiki/Base_bleed
For your purpose I agree with skyking. First reduce drag by creating as small wake as possible using fairing and other "conventional" techniques, than fill the rest with exhaust gases and see what happens. I personally would not use anything else than exhaust gases, since everything else to scoop and duct more air into wake will most probably create additional drag.