this is hard but there is an easier way, just go to the front of the stairs (with the gate blocking the way up) and run at it and instead of jumping straight at the stairs jump to the right side of the railing and jump and duck in the air. this may take a few attempts but it was nothing compared to the time i spent doing it the way outsider did it. if we make a video i will personally do this map for you to demonstrate
PSN: beane13
i am on ps3 not x-box sorry