This method requires roof-running similar to the IWHBYD skull. You will need to first trigger 6 unique checkpoints, as follows:
1. At the very beginning.
2. Walk through the door, get on the roofs, follow around and get to the top of the roof near the bridge. Wait in the corner, appears as the ship arrives.
3. As the ship leaves.
4. Jump down to pick up a plasma grenade from one of the jackals you've killed, and another checkpoint will appear.
5. Grenade jump back onto the bridge, and then grenade jump onto the roof of the next area. Turn left and follow the corner to unlock the next checkpoint.
6. At Hotel Zanzibar, kill the elite and the grunt, and crouch on the building to get it to unlock.
Once you've triggered all 6 checkpoints (shown in the video), you will need to drop down to street level, find an stealth elite and stick them. All elites will turn invisible if you follow them for a bit. You can stick them from a distance or from up close, and reload the last checkpoint if you fail!