I knocked the front trim ring (lower part of the front bumper) partially away from the black cowling piece that sits inside the bumper on my 2007 Boxster S. It is very difficult (essentially impossible) to get enough purchase on the cowling piece so that you get the tabs on the two pieces to connect together. Talked to the Porsche dealer (~100 miles away) and they indicate that you need to remove the bumper.
I followed Loren's excellent video as a starting point to remove the bumper and offer the following comments which differ slightly from Loren's video for his 911.
1. The cover