You use stout shock cord and very short little loops (perhaps 2-3" in diameter). Because they are loops, you effectively have double shock cord. When you set up the tent, you pull the guys snug, so the shock cord is stretched slightly. When wind gusts hit, it stretches a bit more, but softens the jerk.

The method has worked quite well, in my experience. Way better than tying the guys directly to the fly.