I decided to go with Jim's idea for my (first) attempt. It took about 3-4 times of lining up the cling wrap before I got it to line the grille with a good seal so the foam wouldnt get on the paint. It's drying right now but here's a pic of it while it's drying.
In fact, it's expanded quite noticeably since I took the pic about 10 minutes ago. The can says it fully sets after 8 hours... so I probably won't have any updates until tomorrow.