A variation on the good method proposed by cooper101183 in Chapter 7 of the game.
I found it quite difficult to keep DP alive when facing all the enemies, especially with the "shielding" guy and doing this on my highest-difficulty run.
Nonetheless, there is another method that I found easier to get the cheevo. First of all, get the attention of the guys by shooting a guard. Be careful not to kill the "shielding" guy, you'll need him! Immediately after starting shooting, the "shielding" guard will run towards you, since his only weapons are knives. At that moment, backtrack to the lower floor where you came from, and he will follow you. Nonetheless, he does not have the ability to climb back.
Once you have him "secured" in the lower floor, kill the rest of the guards, and proceed to meet the heavy guard/monster with the ice machine gun. Do exactly the same thing. Lure him into the lower floor and, once you have him there, climb back. Both the heavy guard and the "shielding" guard will stay there. Clean up the remaining of the guards that might have spawn (you don't want them messing up with your combo!).
And now, sweet revenge. Take out your shotgun (fully loaded, and up to its maximum capacity) and unload it on the heavy guard. I even needed some extra shots from the LMG, but you can even get to a +400x combo before he goes down.
See the clip from my gameplay.
Cheers!
Sorry, this Game Clip has been removed