Hey guys I just realised how to do the karachi elevator (the one where you can go under map and get marathon and lightweight)

Sorry I don't have a video but here a little guide that may help you do it.

1) Go to the elevator location and stand on the wall facing the building
2)walk as far forward as you can and stand parallel to the wall
3)move to the left (NOT turn left) until your sight is in line with the edge of the wall
4) crouch then turn to the left and try and go prone, keep on doing this untill you go prone.entually you wil start floating.
5) now its the normal elevator stuff go right untill you can stand up then when you can't stand up go left eventually you will start going up. well done

notes:
If it says 'prone blocked' then start again something went wrong
if you can no longer move to the right or left try again something went wrong.

hope this guide helps