Ah, I thought inline installation meant something else. You have two options:
- List the add-on on AMO. This gives you a public URL you can point to so people can install the add-on from AMO.
- Don’t list the add-on on AMO, download the signed file and distribute it yourself.
It’s not a one-click experience, though, because the add-on is being installed from a site that isn’t whitelisted.