I been wondering about this. It should be possible to make a square duct to funnel air onto the cooler, making it the dimensions of the bumper hole, going to the side area of the cooler like a back to front square funnel. If it almost mates snugly up to the cooler you can put rubber edging round the inner end so it doesnt damage the fins and mesh the front so it doesnt pick up stones and chuck them thru the alloy cooler core....not good.
The grille really protects the cooler from this happening but a straight duct and mesh would be better for power.