they sell some nice re-creations of marine invertebrates now days, and they seem soft and rubbery, so I don't know if coraline would be a problem on them or not. but when you get right down to it, coraline, or nuisance algae is going to be an issue for him anyhow, depending on how well he cares for the tank. how about instead of using dead sps's or fakes, you opt for some nice macro algaes? there are some gorgeous red ones out there, and they would actually contribute to the tanks health.
"Maybe in order to understand mankind, we have to look at the word itself: "Mankind". Basically, it's made up of two separate words - "mank" and "ind". What do these words mean ? It's a mystery, and that's why so is mankind." ~ Jack Handey