To me this is a failing of the current market ward interface. You can set up buy orders for your retainers, but they're extremely cumbersome and far more difficult to set up than they should be. Maybe I'm missing some options, but as far as I can tell not only do you have to already have one of the item in your retainer's inventory, but you can only offer gil or a single item in exchange for the finished product. In other words, there's no way to offer an exchange like Mihana described.

I like normalforce's suggestion, however. I would be happy with either solution. Unfortunately, Yoshi seems to consider crafters to be second class citizens.