J.V.
I used to nanny for a kid who did the sme thing. It started with it happening on accident then he started makin himself do it b/c he realized he got attention. ( he had a new baby sister around this time) When they throw up just like with anything else we react and its a big reaction so they like the attention. it took his parents completly ignoring it. I mean not even cleaning the kid up for a while, to get him to stop, but after a time or two of that he was fine.
HTH