If you search "nubbing buckethead" on YouTube, there's a couple guys that have done some decent tutorials on nubbing. It's actually pretty difficult and very few people take the time to learn how to nub like Buckethead does. One guy in particular (British I think) has a few lessons about nubbing, one of them pretty close to that tapping riff if I remember correctly.

Sorry I couldn't be of any more help.