Update!!!!! Picked up a new piece of towing equipment today.

I think if you could get one mounted that went from the top of the windshield and angled back so it came up to the top leading edge of the 5th wheel you'd be good. That would give you a smooth flow of air from the windshield back.

But that won't happen, what you'll have is air spilling over the top of the wedge and hitting the fifth wheel. It'll move the point where the air flow hits the 5th wheel, but won't do a lot ease your movement through the air.