On this level, take a Sniper rifle and a Spectre and boost on the wall near the rocks and the spotting area for the Carbine and Battle rifle. It will take you a few tries. By holding A, you can do a wheelie, which will allow you to have the bottom of the Spectre on the wall. Speed boost and wheelie up the wall (it may take you a few times to perfect the maneuver). Once you are on the side keep on boosting and go left, which will take you to the unreachable area, a perfect sniping spot.