Considering the data I've got on the Stillen intakes, I think it's safe to say that if you're going with the Stillen Gen 3, you don't need any kind of body mod to feed them cold air, they suck cold air just fine on their own:
Intake air temp data (Stillen Gen 3, need stock)
One guy tested his stock intake and saw slightly higher relative temps with the stock intakes, but not by very much (we're talking like 10 degrees). I doubt cutting holes in the bumper is worth it performance-wise, even on the stock intake.