I watched Yngwie do that over and over, and it's totally cool... First, you need a wireless thing, since you'll get tangled up in your cord... But seriously. You don't really throw the guitar up in the air, you take it from under (where you plug it) and you push it over your left shoulder. Due to the weight, the neck should go down, while you are still holding it. Then, release it, and because of the way the guitar is balanced, it shoud come back right at its spot. So, don't throw or push, just release it from OVER your shoulder. Doing it fast it might look like you throw it...