I have tied a fly that was made more than tied using pine needles, little pebbles and other material normally found on a Periwinkle. It wasn't hard to make but was kinda messy. I did get a couple trout to hit the ones I made in a local river.
I think they would work well. Around here the trout always have some alder male cones in their bellies and they look almost the same. No reason to think that these moth cases don't get blown down into the water in a good wind and I am sure that at least some fish have figured out that they are edible.
If you want the instructions for the periwinkle I will try to find them or I will type them up again and send them to you.
I love taking my kids fishing, now if I could just manage to fish at the same time.