Sorry if this has been posted before, but I have seen plenty of cars with license plate holes in the bumper on these forums so here it is -
http://www.bumperplugs.com/BPindex.html

I was pumping gas today when a 911 GT2 pulled in behind me and I noticed his bumper had a couple of plugs. It didn't look great, but it looked better than a couple of holes. I asked him if his car came like that or if he bought them and he said it came like that but he told me where to find it online. Hope it helps someone...