I think I would put them into paper bags and store in the cold dark basement for the winter. Plant in the spring. This is what I've read that many do in your cold winter zone. The reason being when planted late the beardeds haven't had enuf time to grow a strong root mass that will resist winter heaves.

I also would not try to rescue every rhizome but select 1-2 of the fattest of a connected network of rhizomes. 20 feet is a lot of rhizomes!! Good luck.

Well, I have moved them into November once here & even had some bloom the following year. they were some heirloom iris I had more than I needed & you can hardly kill. You might want to experiment with a few & try it, you will certainly have enough rhizomes. I would probably do as irisgal suggested & store them somewhere cool & plant in the spring at your leisure.