Wow! The Pekin Duck Club has been as busy as I have! Took me a bit to catch up on all the posts!
Ducks feather in a lot slower than chickens...
I started giving mine peas as their first treat (frozen thawed) - just don't overdo the treats and make sure that they can get some grit if they are still in a brooder.
Hmmm... don't know about Khaki/Pekin but I have my silkie hen sitting on 7 ducks eggs right now that are going to be Rouen/Pekin!
This is what I get for all my chickens and ducks... and I ferment it, which makes it last even longer. Even if you don't ferment, just wet it. There's no waste when you wet it down and it's organic/non-gmo which is what it sounds like you are wanting to do? You can check if there's a co-op drop in your area - no shipping! If you can find something local, you can easily feed an organic grower or flock raiser for chickens - you don't need a specific duck feed, in fact, most people just use chicken feed. Just add some extra niacin to his/her water once in a while if he/she doesn't have a lot of access to bugs, etc.
http://www.azurestandard.com/shop/product/1046/
*They are currently out of stock but are due to have more in by next month's delivery time - it's about $33.