This is easily done with 3 people and also perfectly comboed with the Team Effort achievement.
Set up a team of 2v1. The person who needs this is on the team of 2 and gets killed. Then they respawn as a zombie and kill the person on a team by themselves. Pop! Two achievements at once in about 1 minute (you just need three people).
While setting up a team match is required, you do not require a full 2v2 to start the match. This method is best done with boosters and not pugs.