Got it on my 2nd real attempt on getting it. I used method 2, it seems to be easiest, in method 1 and 3 you have to be DEAD on the map to get the right area, but method 2 is right at the start, heres some tips to help:
1) Take out the buildings behind the metal sheet. I took it out just incase I touched it and ruined my streak.
2) Do not attack FBI agents who come from behind or from a rope behind you unless they stop, I did it 3 or 4 times and almost failed to grab there head 3 times... its risky
3) As soon as you scare one by pressing X, go above him and press A to keep him there till you land on his head.
Method 2 was easiest for me but we all can't be the same right?