Take injector without plunger and insert it into chamber of cartridge that you are refilling. Get needle as far down into chamber as you possible can. Set cartridge, with injector sticking out of it, and stand it up, or prop it up, somewhere with opening of injector facing up. You want this thing to free stand on its own because your hand will go numb if you had to hold it because it could take up to 10 minutes or more per chamber for ink to drain into cartridge.

Now take other injector, unaltered one, and load it with proper ink in proper amount for chamber you are refilling. Carefully fill cavity of injector that is sticking out of cartridge. Now you wait. Let gravity pull ink from injector into cartridge. At first it will seem like nothing is happening. Go grab your favorite vice, cigarette, beer or coffee, whatever hits you. :-) When you come back ink should be drained into cartridge. Rinse and repeat. And I mean that literally.