ducts are not meant for a visual purpose,they are meant to direct air to the intercoolers.That's why they are molded and painted.To draw less attention to them amd still be tasteful.Not only that,but to duplicate that would not be possible with just bondo..It would have to be done with fiberglass,eurethane, and a lot of trial and error to get the fitment right..Are you fimiliar with the duct in question? To duplicate it would take hours without a mold..I asked my body man about doing them by hand and using bondo today,and he chuckled and said"your serious?" "not if you want it to last."