This actually is possible to boost with a little patience and borrowing some techniques we have all used from the past...
* 4 people with a guest account signed in (substitute live players as needed), All 8 people can be in a party chat
* Split into (2) parties of (4) people each (all party members should prefer each other to increase likelihood of matching
*All players should set default characters to Minh / RAAM
* Both hosts search for standard quick match in the playlist ALPHA - This is a 8 player game mode that you can still select what character you spawn as, and has minimal people playing
We did this last night with great success. With fewer than 350 people playing the game type worldwide, our odds were pretty fair of getting matched up.
We had to actually do this twice as the achievement glitched out for me the first run. Both times we matched up in under 15 minutes of searching. Both times one of the parties landed a room with all bots, and the other party continued to search until landing in that room.
Once your in, your can trade matches ad infinitum until everyone gets there execution kills. Shouldn't take more than two matches.
*whitedragon40k makes a good point: We did use two hosts from the same region, same as Gears 2.
*Nice Add from fallouthirteen to speed matching up: If one group does get put against all bots, the host of that group can leave the game (thus breaking up the party) and re-join session in progress on one of the people still in the game. Since the party was broken up, the next match will split up the group (some members on both teams). From there just have the remaining people join session in progress on the people in the game and there you go...