I watch too much Food Network, so I know that bakeries can also make edible shells and spray paint or brush paint them with edible color to make them look realistic. The shells on my cake were actually supposed to be chocolate shells. But much the same way 3 tiers turned into 2 tiers, chocolate shells turned into real shells. Good thing I was pretty easy going about the cake!
Check out this example:
Have you seen the chocolate seashells? They add a nice beachy feel and are (I'm sure) delicious. At least you wouldn't have to worry about anyone biting into shell pieces! Here's the site...