The aerodynamicist Hucho once mentioned 'reenergizing the dead wake' in one of his books as a method to reduce rear end drag without the added size of full boattailing.
AFAIK he only mentioned that but he never elaborated on that.
Please correct me if I'm wrong.
I just found this technical paper
http://www.vortaflow.com/consulting/...0reduction.pdf
It mentions blown boundary laters, aero 'boat-tails', longitudinal traverse and swept grooves, porous surfaces and vortex generators as means of getting a virtual boat-tail.