I just ordered some Tyvek for my first real DIY-a pair of rain mitts...so I peruse the DIY forum admiring all the genius here and not that I'll ever attempt a down project I do look at the techniques used to instill the down into the baffles.
So I'm curious if this method would work-get the plastic packets of down from your supplier, cut open, then add water, fold the plastic over to contain while you shake and slosh. A clump will form, a solid little mass of wet down. Then simply place the glob into the baffle. After the baffles are sewn then into the dryer on tumble with the tennis balls.