The key you use should be mentioned in the commit message.

I like this approach, because its similar to the commit-msg hook that Gerrit comes with; you install it in your repository and it always updates your commits.  The downside is, the hook fires even if you don't want a Change-Id in your message.

But I'm not sure that is a problem.  I think if your upstream is using Gerrit Code Review, you probably just always want the Change-Id automatically inserted in any commit you make in this repository.  At least that's my use case.  :-)