I have no idea why that's on youtube -- he seems to be just doing exercises; I think he's having a laugh, in part, and practicing "exotic scales" or something. The lessons on his site emphasize odd scales, anyway. Even when doing "real music" he does tend toward the noisy for some tastes, but sometimes plays real purty. Acoustic too. And yeah... he plays with Manring. In fact he recruited Maring by just sending some scores and asked for Manring to play in his band, and Manring thought it was some of the most interesting music he'd seen. So... he does know a thing or two. No MMS on youtube, though.
But I posted a Manring vid here, guy playing three basses at once, that got a sort of similar reaction to this. Wanking partners, no doubt!
McGill used to be in a prog-band called Finneus Gauge, and was a sort of Holdsworth-sound-alike in the fusion band, Hand Farm.
The noise, though, also sounds like much of what Buckethead has done (esp. on Cobra Strike, or his video-game sound-effect stuff). Maybe that's painful to listen to, also!
And that elbow-thing looks impossible, to me. But that's why I picked this clip -- just to ask!