There's a little trick to making this trophy way easier. When you're on the last life and die which would otherwise result in a game over, mash X as fast as you can as you die and the game should continue with another 7 lives. You must also have 500,000 points for this to work. I found dying on purpose in the 2nd last or last room before the boss to refill all your lives is best, that way you should have 500,000 by then and go into the boss room with 7 lives.