Have you considered only adding webhooks per-repo, and not globally? I have access to numerous repos that I don't want or need real-time updates from, as well as repos from organisations that have added me which I would really rather not touch. They would probably not be happy that their repos are suddenly sending data to a third party that they didn't consent to.

I would love something like Ship for my main public repo, and in fact would prefer to just use Ship for that repo.