After almost finishing everything else, I was on 30/50 Super Elite kills and was trying to think of the fastest way I could get another 20. After trying out a few levels, I remembered this part from the Campaign in: Episode Two - Tower Of Hellfire. I also played on Cadet with Enemy Setup for 1 player.
Once you begin, run past everything in the first area until you enter the area just outside the first building you need to go into, then start killing the zombies as you make your way inside (watch out for the suicide ones). Once in, go through the doors and you'll trigger a checkpoint. Now, you want to clear this area so the fog disappears which is blocking the next area. The fog I'm talking about is the one where a Fire Demon will come out of first. Once this is done, you'll trigger another checkpoint when entering this new area. This will be the checkpoint we'll be using.
Now simply follow the path and kill the suicide zombies which will run at you and as you near the corner, you'll see a wheel and a zombie to the right of it, hitting some pipes. Carry on going past this and you'll encounter a Super Elite. Defeat him and then go up the small staircase in front of you, go left and follow this walkway. As you near the end, a Super Elite will spawn ahead. Defeat him too and then restart the checkpoint and repeat. Also, just be careful not to sprint all the way down on the walkway as it sometimes makes him not spawn. If you do by mistake, just backtrack on it a bit and he'll spawn.