Thank you, but I customized a (folding) bike, and as a result, the bolt tends to move a bit outward after I fold it completely. Adding an inline barrel adjuster seems like an easier fix until I get home and reposition the bolt where it's supposed to be. A bit kludgy, I agree, but better than filing down the frame to fit Shimano's non-turn washers.
Elsewhere, I read that, at least, the adjuster should not be located within a curved section, so I'll set it up right before the cassette joint arm, and see how it goes.