Hi Folks,
I'm late on seeing this post, but as a "Master Underwater Vomiter", I highly sympathize. I have tried all sorts of medicines and tricks (those patches make me faint), but finally have had some success with a homeopathic medicine called "Cocculine" in France (it's a combo of "cocculus, tabacum, nux vomica and petroleum", whatever that means). Even with this, I sometimes get sick (although I don't get as sick when I'm taking photos, so this problem could be psychological).
But I was surprised to see how others "vomit underwater". When I see it's coming, I take the reg out and do it right there. (Although on land, you reflexively inhale afterwards, underwater you don't.) I then put the reg back in, exhale or purge, and next start photographing all the fish that come around!
Good luck!
Tricia