I might be confused here, but local::lib does not deal with CPAN mirrors. It deals with installed modules.

If you want to run your own CPAN mirror, using a file:/// URI makes the cpan tool use a fileshare instead of HTTP.

I think that App::cpanminus (for example) can deal with non-HTTP mirrors as long as they have the usual CPAN structure.

If you meant something else, I'm sorry that I misunderstood.