Configuring Annotate for Multiple Databases

I’m creating isolated engines with separate databases within an umbrella. I’d like to use the annotate gem to generate the comments for models and factories, but I can’t get it to work for more than one engine. I’ve tried specifying --model-dir pointing to the other engines but that doesn’t seem to help. What am I missing?

bundle exec annotate --force --model-dir /path/to/models is the command I’m using. Where can I specify the other databases for it to check? I can’t seem to locate any documentation on this subject, though I’ve seen others achieve this.