I think I've got a fix, what do you think? The "feather the selection" just produces a fat line due to blurring/feathering so I went even simpler and created a striped stroke of solid black with varying opacities (see screenshot).
JFJ -- Creating paths from selections then stroking that path is unreliable a lot of the time; it never seems to stay true, it rounds off way too much. Of course it could be something that I'm missing but the path never has the same detail as the selection (see screenshot). So I try to avoid paths.