[aerohead]

That's my plan also.
Road vehicle aerodynamics requires a turbulent boundary layer to control flow separation.The kinetic energy fed into the boundary layer helps pin it against the body,preventing it from migrating forward to the body's zone of minimum pressure (at the windshield peak) and rolling up into eddies,then full-blown turbulence and separation.
A plasma adjacent to the body surface might ruin the whole feedback system.
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Aircraft and aquatic creatures have fineness ratios which prevent flow separation in the first place and their drag is governed by surface friction or shock wave drag for the fast aircraft.
Not so for automobiles.
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If I were gonna consider plasma drag reduction I'd look to high-speed trains whose boundary layers,according to Hoerner, can be thicker than the frontal area of the train itself.