To "hide" the posts from your flist, you could "date out of order" on them. The posts won't show up if you do that, but you'll want the Master Post to show up on flists.

It's a double-edged sword - when I did that, my flist didn't see the fic for the most part. On the other hand, well. They didn't see the fic. IDK, it's your call, but frankly if you space out the posts over a couple of hours, it should be ok, haha.