don't know the setup for yours but I was just at one recently in Daejeon (been here for 4 months before that) and yes, alcohol is banned on the campus we were on, but just go out to a bar at night if you feel the need to drink. that's what most of us did. I didn't hear about anyone causing any problems when they got back to campus out of our orientation group.
yes, koreans do drink at training events, but here's the difference: they say on paper it's a "teacher's training" but when they get there, no one actually does any training or attends any lectures, calling it a teacher training is just an excuse for the staff to take a short trip together.
as for us? we're at those orientations to actually learn a bit about our craft, get good ideas, network, etc etc, and also to learn a little about korean culture/language/how to adapt. believe me there is noooooooooo shortage of time for people to hang out and drink and party for the remaining 362 days of their contract.
suck it up for a few days, during the daytime at least. i'm sure your liver won't go into withdrawl.