The easiest way I found to get this achievement was by playing as Saint on Strikeout game mode. When u start the match focus on leveling up your C4 to max so they are harder to see and you have 2. Next plant both of them on the site or a heavy traffic area. Then run to a zip line and simple keep going back and forth on it until someone runs into your C4.
Skyfell: two small zip lines on either side of spawn (safest and where I got mine) and a long one (high risk, in the middle of the map off to one side).
Falelas: one very short zip line in the middle of the map in the canal area. Probably not worth trying on this map because its so short, imo.
Windward: two long ones on the left and right. Both are on the side with the grassy courtyard drop area. This is probably the second best map to try due to the zips being in a medium risk area.
Icarus: no ziplines
I'll update with the other maps that have zip lines as I play.