I just finished our second session for this yesterday. This is a buggy achievement, but we managed to get a strategy going where we popped the achievement for all 3 of us that needed in 3 games in a row!
(in both the German and Japanese version for the record, but should work on all versions)
Have the person going for the achievement host the game. The best map is factory as it is a really small map (if you're also going for the truly inspired), also make sure to set the round preparation time to 10 seconds to speed things up. Also, friendly fire ON.
Have the host set preferences set to: (IMPORTANT: AFTER EVERY MATCH THESE RESET, EVERY TIME ONCE BACK IN THE LOBBY HAVE THE HOST SET THEIR PREFERENCES TO THIS AGAIN)
Squad leader YES
Tank commander NO
and other option NO
All other players have their preferences set to the default NO YES YES
The Host team will be winning, this first game have the opposite team suicide by throwing grenades at their feet (friendly fire is on to increase chances both players die quickly)
(host set preferences again)
Be sure that the p;ayer on the host's has pressed
to vote for the leader to stay in command. Once the match starts, the host will earn the earned in blood achievement.