Start a game on normal, and proceed to the point where you need to cross from one ship to the other via a beam. this is the first time (that I found) where, if you actually fall, you die. Do it. The game will restart right before the beam.
Do that 5 or 6 times and the game will ask you if you want to try it on easy. The trophy should pop when the option is given.
PLEASE NOTE: I tried doing this on Hard at the very beginning and just letting enemies beat the hell out of me. After about the 15th time of starting over I realized that method doesn't work. You have to actually make a little bit of progress in the game before this option is given.