Bone, a lot of good advise mentioned. If you can find it at your local super market, pick up some "Sudsy Ammonia", and inject as Elkstuffer mentioned. Also, once you get the skin around the bill off, inject as you go until you get that skin over the head to the neck. Be careful around those eyes!
If your not going to flesh right away, soak in Dawn and Luke warm water for about a half hour, then wrap it really good and put back in the freezer. If you let it sit out for any length of time, you will start getting feather slippage which is not good. Freezer burned skin is notorious for that. Hope that helps.
By the way what kind of ducks are they? John