[Feature request] Serving custom html only for 404s

[Fukitsu]

Right now if you specify a custom index file it will serve that for all paths. I'd like to be able to serve a custom index.html only for when an error occurs (404 in this case)

[aliemjay]

Have you tried --spa option?

[Fukitsu]

Yes, but that servers the index.html for all routes instead of the default listing. I'd like to serve only a custom html only for when a 404 occurrs