Well there was a bit of improvisation I used a standard drill with a wider drill bit to put 4 or 5 small holes into each honeycomb shape, then got the dremel in there to clean it up into 1 honeycomb shape (if that makes sense). Then used a bit of sandpaper to clean it up, took a little while but still better than paying $200+ for the proper ones.

With fitting the duct, I used araldite and left it overnight, then some black 3M tape to bind the two together and seal up any air gaps between the two pieces. There wasn't too much mucking about and they all fitted back in to the bumper pretty well. Also, surprisingly didn't have a whole of trouble getting the old lower grills out either.

It's worth it in the end if you're considering it, as I know it's something I've put off doing for well over a year.