Have used this method to help get a few friends the ach very quickly...not 2 people, not 4 people, but 3 people playing Alliance in private.
This achievement requires open conflict, which is your target being chased by you, while you are being chased by a pursuer. Super simple to boost, just meet somewhere on the map and all 3 of you run around in a big circle until everybody is both chasing and being chased. Stop running (so long as you stay within site of each other, the open conflict situation will continue), hit x to kill your target, hit b to stun your pursuer and achievement unlocked. Repeat 2 more times dying once, and getting knocked out once, just remember to get into open conflict (chasing and being chased).
This method works great to get it done very quickly (all three players should be able to get it within the first minute of Round 1).
This will also unlock the Fast Learner achievement if you do not already have it, so long as you stun within 10 seconds of getting the kill.