A bunch of us were trying to do this yesterday and it was difficult with all the random players that would join. There are a few factors that should help though, even with randoms. Most importantly, you can still be killed by a different player than the person who you are trying to nemesis. So it should still be possible for a dedicated pair to slowly rack these up.
I would like to propose that we find a remote area on each map where we are less likely to encounter random (fighting usually occurs near the center of each map). We can also make use of ninja smoke bombs to avoid interference from other players. Finally, we decided that bounty hunter was the best mode for boosting.
So what do we think. Can anybody pick out some good map locations? For example, on 25th floor, one of the balconies behind the building would probably suffice.