You'll begin with learning to scan the remaining bill and figuring out a proper attachment interface and adhesives. Then a matter of material choice. This may depend on the printing process you choose. For the one-off's you'll be working with, you might ask yourself if professionally printed prosthesis would serve the duck better than trying to make a hobby printer do a makeshift job of it. You can certainly get to a good prototype with a hobby printer, don't get me wrong, but in the end, a highly refined 3D scan and a very close fitting, thin member interface will be critical is adhesives are to be used. I want to say that an SLA printer would be ideal for fine details and a solid build but i am not sure of the material choices and which printers would come up with the best solution. I will give the Form 2 "Tough" kriptonite green material a nice choice for ductility (no pun intended there!) but I don't know how bio-safe it is in the end. Good curing is a -must- with all SLA prints if it has anything bio associated with it. Did I loose you completely