If you want my method, with the left hand I hold the left-most button (green-red-yellow-green), while my right hand taps the rapidly alternating frets (ex: yellow-blue-yellow, with index-middle-index), all with the lower frets. Since it's all hammer-ons, I just release all fingers to play the beginning fret.
So at the beginning, I hold the green fret with my left index, while my right index and middle finger tap alternatively the yellow and blue frets. If you master this, you only have to move your hands slightly and do the same thing, but with different frets. I'm currently practicing it, but I know I have a method that fits me well. Oh, and since you play on expert, I don't think I need to explain about the remaining parts!
