The only solution is to create the faux API call to define the API object. Once you define the API object, you can then use it within your plugin. If this is a plugin just for your application that can work, it’s not a great solution if you plan to distribute it as everyone of your users would have to manually define the API in their application.
This is in my opinion (and others) one of the most limiting factors of Bubble extensibility and it doesn’t appear to be on the roadmap to be fixed anytime soon.
The long discussion and example on this post: