I have a kolsh recipe that has a maltose addition and I just add it about the last 5 minutes of the boil, as long as it disolves, it really doesn't matter too much, it's just a sugar addition and doesn't do anything for flavor, just sweetness and body. The last 5 minutes or so should be fine, just be careful it doesn't go to the botom and burn. When I add the maltose, I just gently stir it in so it does sink and burn on the bottom.