The pilot's comments are in Italian, but even if you don't understand that it doesn't matter. This is another in the category of things I would be afraid to attempt myself but am amazed to see someone else do. You can see a map of the flight route to get more of the (incredible) idea. Sample:
Back to drear shortly.
This article available online at:
http://www.theatlantic.com/technology/archive/2011/11/to-lighten-things-up-glider-flight-across-the-alps/248991/