Use of duck fat at the time of cooking? 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.
I think the usual use for drippings is incorporating the fat into a gravy or pan sauce.  A bit of flour, a bit of water, salt and whatever seasonings.  I don't recall if it is common for duck specifically, but I see no reason it an't work.

As for your pastry idea, I don't think it usually works that way, the physical disturbance of the dripping and the uneven distribution might make the pastry texture not come out quite so well. (I assume there's a reason pastry isn't commonly used to catch drippings).  

If you still want to try something similar, you might be interested in yorkshire pudding - which was historically used to catch and use the drippings from a roast or similar, and being intended for this purpose it will probably work better than a random pastry recipe.