My 1978 Trek has a chainstay cable stop that fits only the housing itself, with no room for ferrules. I'd prefer to use a ferrule, but can't, and I've suffered no adverse effects. That bike is friction shifting, but so long as you're using compressionless housing and getting it tightly seated in the stop, you shouldn't have problems with indexed shifting. That doesn't help if the hole in the stop won't hold your cable at all, though.