Guys, this thread started so nicely, please don't corrupt it by TROLLING.
"This can't be done" attitude is trolling in my book, and if i were moderator I would delete such posts.

"Dirty air" for a pusher is in reality just a minor problem, and nothing to get caught up in.
It is not caused by turbulence either, as propellers is in reality very insensitive about turbulence.
(Ex. think about counter rotating propellers, or coaxial helicopters. The rear/lower propeller/rotor is constantly running up close in the turpulence of the propeller ahead, and it is practiually unaffected by it).
The thing with pushers is something called P-factor, which is a shift of vector direction and length in thrust when freestream into a propeller hits the propeller at an angle other than parallell with spin axis.
For a pusher, this angle might be different depending on where on the propeller disc you measure, because the freestream direction vector is different on, for example, on the upper side, and the lower side of a wing of which the propeller is mounted behind.
This difference in P-factor on upper and lower half of the propeller disc is causing a minor efficiency loss, and some extra audible noise.

For all practical pruposes this efficiency loss is NEGLIBLE unless you got SEVERE difference in P-factor from upper side to lower side.

(ex. think about a helicopter. When its moving forward at lets say 15 degree pitch attitude, your freestream relative to spin axis angle is 90 - 15 = 75 degrees.
But the rotor still works, and the helicopter flies. For an aircraft with pusher, you will never ever encounter p-factors as a result of such extreme freestream angles).

Long story short: Stop Whining, pusher isn't a problem! Stop derailing a great project with neglible "problems"!
Stop being surrender monkeys!

None of you guys got acces to neither the equippment nor the knowledge that the designers of any full size pusher aircrafts do, so the fact that full scales can measure a difference in efficiency doesn't mean that YOU can. and if YOU can't tell the difference, YOU can't care either.