I dont have the CD on me right now, but if its what I think it is I can help.
Its called a vibrato arm "flutter", basically, you can only do this with a floyd rose-style trem thats floating(in other words, you can pull up on the bar too). Basically what you do is put a little pressure on the bar and let your hand slide off, giving it a little "flick". Picture your index finger is the bar, take your other index finger and place it around the 2nd joint and press down a little and slide off the tip of your finger...notice how your finger kind of "vibrates" a little? Thats how it gets the "warbling" sound, from the bridge vibrating really fast. You'll need to mute the other strings you arent playing tho, or else you might get some of the other strings ringing out. It takes some practice to be able to do it like Alexi does, but its a cool effect.
Steve Vai does it a lot too.