Pewter finally delivered her babies, on the wire, while I was at work. Nine in all, and I was able to save three.
When you find a new litter scattered on the wire, don't assume they are dead, unless they are frozen solid. I scooped them all up and into a bag, and took them into the kitchen. I ran very warm water into the sink, a couple inches deep. Then I got sandwich bags, and placed each baby in an open bag and set it in the warm water. They float quite well. I sat back and watched. One by one, four of them came back to life! After they had invigorated pretty well, I placed a plastic container in the water and placed the four warmed bunnies in it, and went back to Pewter's cage and gathered the scattered hay and wool and put it in the nestbox where it belonged, making a bowl in the center. I then cut up some angora wool from my stash and lined the bowl with it, then got the babies and put them in, covering them with more wool. For good measure, I took a very toasty baby from Sunrise's litter of nine (I mis-counted them, or she had another, I'm not sure which) and put it in with them.
An hour later I checked in on them, and three of them had scattered. The one that snuggled with Sunrise's baby was fine. I gathered the cold ones up and put them in my bra. Don't laugh, it really works! Anyway, two of them revived. I put them back in the nest. Another hour went by, I checked on them again, all were snuggled and warm. Now it is up to Pewter. Hopefully, she'll be a decent mom. If not, Sunrise may have one huge litter to raise!