this is a tough one. As an instructor, I have a great beach with really shallow water, but for my personal riding, I sometimes use a pretty sketchy launch with deep water, and rocky/shale launch area. More often then not, I'll set up the kite at the edge of the rocks, run out my lines, then push the kite in the water, run back to the bar, leach attach and then spend the next moments in fear that the lines will wrap under a rock causing issues. But lately I've been using a spare leash to tie off to a small tree or rock, hook that into the bar and I run out the kite to the edge. No issues, no worries.
Another option for these guys... how about tying off the bar to the anchored boat once unwrapped, and running the kite to the edge? That way both student and instructor can be in the same place. I think it's one thing to explain to a student what is going to happen versus coach them through it, AS it happens.
In normal beach launches, if I have two students, One holds the kite while I coach the other on how to launch, then we trade, then get into the water and do the rest of the lesson. Either way... hats off the the deep water guys. I have no doubt that there are a lot of variables to think about. Anyone read that story about the lessons in france that resulted in a death? TOo many students, too many kites, one boat, one instructor and all bad news. be safe out there.