I've tried this only in White Lotus Hotel in Shinjinku where you can loot the gi green suits. They have a speed mod, force combat, some resist, and reason.
Just kill the boss, loot it, and DO NOT kill the guards even if their attacking you. Then run through the three doors that you came in (not the teleporter doors) until you run into a metal fence, the guards should run back by the boss. Stay there for until the door closes and wait another fifteen seconds or so. Then run back in and kill the boss again. Rinse and repeat.