Have you tried the ghost shrimp? My fig 8's love to eat them. They'll eat just about anything though. Once in a while I get a stray crab leg from the supermarket (for free), and cut about a half inch piece off and drop it in the tank. The puffers go after it right away. They are actually not that likely to eat snails. I wish they'd eat more snails, as I'm worried about their teeth.
You could also try a clam. I got a clam from the grocery store, cracked it's shell partially open and my puffers ate most of that clam too. I wanted to make them pick at the shell some, since I'm concerned about their teeth.