If the plant material is nicely dry most of the seed should fall out easily. Just a quick rub/knock will do it. Anything that doesn't fall out easily likely wasn't fully mature when harvested. You don't need to break the dried flowerheads to get the seed out. It just sort of falls out leaving a 'cup'.
The real difficulty is in separating the seed from the waste. It is so small and fine it is difficult to get the tiny, white, shuttlecock shaped seeds separated from the rest of the fine material. The seeds and frass are the same weight so winnowing risks losing the seed along with the waste. We used the winnowing machine on the batch we did here last week and still didn't get it completely clean.
Unless someone else comes up with a better answer to your question, I suggest just planting the seed and the waste material together. When the seedlings get big enough they can be separated and planted at better spacings since it is hard to sow such fine seed accurately anyway.