With the expertise already represented here, I hesitate to say anything. But for what it might be worth, I want to throw out there the name of a product that might help. "Gorilla Glue" dries less quickly than super glue, and is water activated. In making a splint, maybe this product could be of benefit. I don't know toxic or not, or whether you could keep the duck still. Seems if a vet could sedate and repair with a splint it might help. No idea, really, so that's all I'll mention. Following, and hoping for the best.