Anyway here's someone doing webfinger with a static file, in a way that works for serving for multiple users: https://gist.github.com/aaronpk/5846789
I’m not sure if you could implement something similar with s3
Sorry, but this is a form of equivocation[1] at best. More honestly, it's a simple contradiction; at the point where you're "map[ping] these URIs, params and all, to static files", then you are already being forced into running a dynamic application.
Although not well-defined, a "static" site is widely understood to be the sort of thing you get with e.g. Neocities or GitHub Pages or one of its myriad clones—where you cannot rely on being able to mess with the server configuration (past the point of, like, specifying the hostname your site should respond to). Any configuration more involved than that moves it out of this realm and towards the dynamic systems that people are largely not running and not interested in running—for various reasons, including pricing, maintenance, and sheer complexity/brittleness. It's a place where you dump a directory of files and the host doesn't do much beyond serving that file with the appropriate media type, i.e. the only thing that people can reliably trust to work if and when they move all their crud to another host someday.
(EDIT: Actually given it does a full regex match it might work; though it'll return supersets of the intended results if rel= constraints are preset, and possibly break if the rel= argument is put after the "resource=" in the URL so would need refinement; of course it depends on using a server which allows arbitrary regex based rewrites, which rules out a lot of object storage etc.)
It may happen to work for some clients some of the time, until it suddenly doesn't.