When I broil breast of duck, I get a significant amount of fat that pools below the duck breast.  What can I add to the dish that will soak up that duck fat and benefit from it?  The only thing I have thought of so far would be to make a pastry. So the idea is that I would make a flat of pastry dough and place it beneath the duck while it is cooking. Then, when both are cooked and the pastry has absorbed the fat, I take the duck out, peel off the skin and discard it, then I put the duck breast back in the pastry, slice it, and serve it. 
Roasting, or rather deep frying in that case, some already cooked potatoes(boiled or steamed) seems like a good common use of that duck fat to me.  I would keep it anyway, and use it as a replacement for any fat you may use in your cooking like oil or butter. It'll be great for roast vegs, either pan or oven. Just make sure you cool it down fast to avoid the "danger zone" between 3 and 60 degrees Celsius, and keep refrigerated. 