Join a public free roam and then invite a friend. Posse up and then create a team deathmatch or any other team based game mode.
Now, when the match starts, have your partner leave, which automatically nets you a win.
Now when you go back the voting lobby, invite your friend to the game again and when the next match begins, do the same.
After your partner leaves the match for the 4th time, you will get the achievement.
PS: make sure you kick whoever joins the match because for a small window of time you and your partner will have the majority guaranteeing the unwanted player is kicked.
This shouldn't really be a problem since the method takes mins and if you are in a fairly empty free roam, the chances of people joining your game are pretty slim.