You can build your own APK of Infinity with your own API key. You don't need to install any apps (other than infinity) and it can be done from your phone.
Screenshot in case the post on Reddit is removed:
Edit: Also, Geddit (Website) (F-Droid) (GitHub) works without the API, but you can't interact with anything, comments don't show properly, and I think the UI doesn't look very good.