Not sure if anyone is actually gonna see this seeing as the last post was months ago... but....
Another way to block the 'bong hole' is to cut a piece of plastic to fit the hole and then melt it in. I did this today and its completely air-tight. Definately a noticeable difference in throttle response too.
Drilling the holes in the grill was really easy and definately worth the 15 minutes it took to get it off the car.
Thanks everyone!
