Start a new terrorist hunt using the following setting:
Map: Kill House
Terrorist Density: High
Lone wolf enabled
Use an assault rifle, preferably with a short range sight, and smoke grenades.
As soon as you start, hold down X. Press left to apply a suppressor to your rifle, and up to switch to single shot.
Run up the stairs to the right of your starting position, onto the roof. Throw a grenade into the center, and let the smoke fill up. Put on thermal vision and run into the center. There should be two terrorists on the roof with you, that you can now easily pick off with head shots without being targeted.
Henceforth, wait for terrorists to make their way onto the roof and pick them off with head shots. Not a too difficult task. For most the part, you should be able to hear any terrorists approaching. If they come up the stairwell, you will hear the door open. If they rappel up, you will hear that too. The only way they can sneak up on you is through the same stairs you got onto the roof using.
Should be fairly easy to make 5 consecutive head shots, especially with the 35 terrorists all sharing the map with you.