Why not get rid of the rear wing completely?
BAR did this with their high-speed prototype, just has a rudder on the end.
"It looks more like F1 cars of previous decades before huge wings" they said.
The rudder was for safety, because that car is on a different "track." However, would getting rid of the rear wing allow for a good amount of overtaking? What about when combined with other techs like regenerative braking, larger diffusers, and active aero? maybe new tire designs? assymmetric tires anyone?