That's a lot of duckfat for this but you could use a couple ounces for this cassoulet recipe and swap the chicken stock for your duck stock, or even mix chicken stock/broth with your duck stock if you need more.I made duck confit. The recipe said the fat was reusable if you strain it, so I have all the fat saved. No bones left for your recipe, but there is still some leftover meat.
https://www.allrecipes.com/recipe/246668/chef-johns-cassoulet/