When BJ disguises himself as Redfield to pretend to audition for a movie, there will come a point where you need to walk into a glass enclosure with a guard. Hitler will be lying on the ground to the left. First off, make a manual save right when you regain control of BJ's movement. Then, before walking in the enclosure, walk over to Hitler and press R3. You'll kick him in the face, and kill him, and then BJ will be killed instantly. You'll get the trophy, and reload from that save you just made seconds ago.