If you are struggling with this, you can knock 3 enemies out (I used fists) pick them up and put them on the floor together, SAVE YOUR GAME and try for 3 headshots. As they are knocked out it should be a one hit kill.
You can also do this very easily when playing as Johnny Silverhand attacking Arasaka both times, just get up close to them and good luck.
I can confirm this method worked in 1.52.