Actually, there is a simpler, if less technically elegant solution. Extending the flaps on most (older anyway) transport category aircraft causes a large number of disturbances in the airflow, including the lateral airflow around the wingtip. Aircraft with 'smoother' flaps have a stronger wake with flaps extended. The poster child for this is the 757, and is part of the reason it is considered a heavy for wake turbulence separation. Boeing (and presumably Airbus) have researched having slight displacements in the flight controls in some phases of flight to break up the wake. It works a charm, I am told, but the certification was problematic. Having said all that, I am very interested in the all other things being equal technical answer.