We used to run lots of free-for-all scenarios with all players playing Marines, and the 'stealers on auto rules coming in at d6 blips per turn through 1 of 20 random entry areas (using a d20).
Each SM player enetered from a different corner and had an objective room (near the other side of the board) to cleanse with righteous fire, retrieve the C.A.T., the Log or whatever, and were free to cooperate throughout. Regenerate squads when they get wiped out, and the player with the highest kill ratio in the allocated time wins!
(thus if you take a replacament squad your ratio halves and you have to work harder to get it back again, but at least you arent sitting around watching and not playing)
Good Luck Marines!
