Someone taking lots of photos and say rotate a sailor per good gyber. So much of it is good entry clean entry into the gybe at the correct angle and you can't really correct that on a boat.
You could have another buoy away from the boat where people can practice what they've learnt from good gyber till their rotation comes around. I don't think much of it is something you can correct in one day, so good gybers have to pick a few points and have their sailor perfecting that.
Simon can run tuition on the beach before hand, and a debrief afterwards if necessary.
BTW nooooooooo, how am I going to catch up if everyone starts making their gybes