Doing this legitimately can be easier than you think.
I am only at a level 7 online, and I was paired up with players who were level 35, 52, 46 etc. - much more than me.
This technique is how all novice players should play multiplayer online in these gametypes - it allows for you to see how the better players play, and also allows you to rack up some points with downs, revives, and kills. Your partner should be getting the majority of the kills using this method, but you will definitely get some as well.
And so what I did was I became a shadow of my partner, the better player, and covered him as he took the initial chances. If he went for the flamethrower and then was rushed by an opponent, I would shoot that guy with the shotgun to buy my partner time. If he was involved in a close fight, I would flank and shoot or melee the other guy with the shotgun. And if my partner was downed, I am right there to finish the opponent off and revive him.
If a two-man team came at us, I would try to kill one of them and he would try to kill the other, and if one of us kills our guy, or downs our guy, we can then go help our partner out, 2-on-1 is better odds. And sure, sometimes this wouldn't work and one or both of us would get killed, and that is the breaks.
With this technique I got the Wingman achievement in 5 games.