To do this, bring a weapon of your choice and C70. It starts appearing on the Hardest difficulty around level 36; try farming level 40 on Hardest). As soon as the level begins, start dropping C70 off the sides of the path and detonating them. Remember that the C70 has a 40 meter blast radius; be careful not to be in it. You should be able to get the enemy numbers down to about 20 by doing this. Then, just mop up the remnants. Note: This also works on Infiltration 1.