Easy way to pass the intro: tie a rubber band around the green fret. Then you can just keep your left hand stationary over the top frets. If you still have trouble, odds are you're not releasing the frets quickly enough. Slow it down in practice mode; if you can play it perfectly at a slower speed but can't get it at full speed, your hand simply lacks the speed/dexterity to play it. Just get more fretting practice, preferably on other difficult songs so you don't bore yourself to death. (You can remove the rubber band after the intro, during the break.)
"Correct" way to pass the intro: two-hand tapping, using your elbow to strum, as described by the above posters. Far more impressive, but many will find it extremely difficult to learn how. Others will pick it up fairly quickly.
