In my parts, sausage cases would be bait, because it is edible. But there is not much difference between that and say rabbit hide strips. I don't know when fishers got all hung up on bait vs. non-bait tho, it's not a traditional concern. Izaak Walton fished both flys and bait.

I have issues with bait because it is messy and stinky. Yes, I could catch more fish if I kept bait in my trout arsenal, and my trotting gear has traditions as long as fly fishing. But I find I catch more than enough fish to keep me happy so I don't need the benefits and can definitely live without the hassles of bait.

Czech nymphing is a very traditional means of fishing. It is simply a form of tight line jigging and the three fly cast is also steeped in tradition, when people fished to catch and keep fish. But again, fishing and fly fishing in particular for me isn't just about catching fish so I don't need the hassle of the three fly cast, and I definitely think that if you're going to fish with fly line, you should actually use it for casting.

So if I ever felt the desire to "Czech nymph", I'd just bring out my 11 1/2 foot drift rod, spinning reel, and my assortment of ultra light jigs, of which I'd use only one.