I found this nice QB drill video, courtesy of the Orange and White blog covering Clemson University sports http://www.orangeandwhite.com/ .
You'll see new Offensive Coordinator Chad Morris drilling his quarterbacks on the bubble screen throwing mechanics to the left and right. I like how he makes a verbal coaching point about a baseball player, which is what I learned years ago when Rich Rodriguez used an analogy of your quarterback needing to be like a middle infielder in baseball on the bubble screen 'turning the double play' on his throws.
Chad Morris working with QBs during Clemson spring practice
Keep spreading 'em!
Spread Offense - How To Run