Step 1: Materials
1. Screaming Skull found here for $11
2. Bondo Body Filler
3. Bondo Glazing & Spot putty
4. Plastic Epoxy
5. Sandpaper 60/80, 220, 400, 600, 800, 2000
6. Tack cloth
7. Primer the kind you can sand
8. Spray paint of you choice. recommend Kylon Fusion because it is made for plastic.
Step 2: Mounting the Skull
After the epoxy has dried mix your bondo. Just follow the directions on the product. You should have a nice light pink color when it is mixed properly. Make sure you tape off the hold on the top and bottom of the case. It will be a pain to get the bondo out of the holes. After you have applied the bondo you can remove the tape. Make sure to remove it before it dries though.
Let the bondo dry for 30-45 minutes.
You can learn more about bondo here.