try skipping lou and playing on expert for a while. once you feel you've gotten comfortable with long hammer ons and pull offs, go back to lou and he'll seem like a breeze
oh, and try not to use powerups too quickly (i kno it's tempting). save up 2 or 3 and wait for lou to go into a solo, and you can hit him for an easy win. imo, best combo is lefty flip and wammy bar.