I did this on Level 1-1, but any level works. Earlier levels are better because of less zombies. Don't fight, just run, and try not to take any damage. When you get to the 3 Boomer wall, just keep going. You will get hit, but this won't affect the trophy. You can get hit up to 2 times before you die. As long you didn't damage zombies, the trophy will pop at end of the level.