There have actually been a few threads on this. I don't think it would be a good idea because you can still have nausea. Also, you cannot vomit, but you CAN dry heave and retch, which is far more painful and scary in my opinion. It's just like vomiting, but nothing comes up.

As an emetophobe, our problem isn't actually vomiting, it's the anxiety we feel about vomiting. No doubt that the average emet would still be nervous if they felt nauseated after the procedure. They would most likely be anxious that it didn't work, and they might V anyway.