765 Trophy in Noby Noby Boy

Hold right on the Left stick and press Start to bring up your real-time stats page with your length. Keep stretching and then shrinking to build up your unreported length. Now watch it very carefully and go very slow once you get around 750m. Once you see that it says 765 get out of that menu and press up on the Left stick and press Start to bring up the Girl menu. Report your length and the trophy will pop up.

(Tip: If you are on a map with any kind of moving objects, i.e. cars, if they hit you while you are close to 765 they will cause you to stretch more and you have to start all over.)