Comment by stephencelis

It actually lets you do this already, though the documentation is relegated to a manpage that doesn't get installed automatically. It checks, in order, for:

  - $GHI_REPO env var
  - git config ghi.repo
  - remote named "upstream"
  - remote named "origin"

So you can just use "git config ghi.repo username/reponame" to get the behavior you want.