I've done it a few times. I just do it on Earth near where you spawn. If you go dead ahead and slightly right there's two dregs and a vandal (usually) in that "corner". Either go up close or pick them off with a sniper rifle. Over to the left, as you travel towards them are those stairs that go down to one of the first missions you did. There's something like 5 vandlas and 3 dregs that spawn there. Again either pick them off from a distance with a sniper rifle or get closer and shoot in the head. Now hop back to the first place and those 3 are back. Deal with them again and by that time the other 5+3 are back. Keep alternating between the two (one "jump" using glide) and you can rack up 200 in about 20..30 minutes.