Has anyone fiber-glassed the hollow bumpers to make it more aerodynamic?

I was looking under my 2010 aveo5 and realized that the car is not aerodynamic at all on the underside. The bumpers are completely open and hollow; it seems like this might create a parachute effect. Has anyone attempted to fill in this gap to reduce the aerodynamic drag?

I think it would be more effective to remove the black plastic piece on the bumper, maybe create some type of diffuser to replace it as well.