Well, I had a revelation last night. (Yes, I admit, the beer helped.) Does a chicken or beef or pork or bean enchilada qualify as a sausage? ...and shouldn't tacos get credit too, especially soft tacos?
After all, tortillas make excellent casing. In some ways, working with tortillas is like working with collagen- - don't wet them too much, or twist them too much, or they'll come apart. However, they are excellent at doing what casings do best, containing the mixture of meat, spices, cheese and whatnot.
Hmmm... Maybe I should make up a couple of batches to prove it. ...be right back. (...sounds of rummaging through kitchen cabinets, drawers, Fibber McGee's closet...)