This one is tough so make sure you hit the checkpoint nearby and quit out of the game when you die if you are taking too long. Run through the boss and hit it with the Kilver from behind. Just as the Flamethrower attack ends, start running right. Now shoot Nova bombs under him and jump over his shots. Unfortunately, there's no other trick here, so reflexes and skill are required.
This method gets you pretty close to the end of the fight but it starts you out with a little less health. Not a great solution, but considering how long and drawn out this battle can be, it should help speed you to the conclusion, be it success or defeat.