I don't usually stretch at all - if you ride enough, you shouldn't have to. I read that somewhere too, I forget where. Maybe someone else can confirm. I usually start slow if it's the first ride of the day and if it's early morning. I just want to get my muscles a little more awake and in tune with the flow.
I haven't done Yoga in over a year but when I was doing it regularly, it was amazing for riding.