Fetching content from file and Ember CLI Mirage

I have a component in my Ember app which returns data from a static markdown file.

  didInsertElement() {
    fetch('markdown/faqs-content.md').then(response => {
      response.text().then(result => {
        this.set('markdown', result);
      });
    });
  }

When the app runs, the request goes to http://localhost:4200/markdown/faqs-content.md and everything works fine.

However, in mirage, I get this error:

Mirage: Your app tried to GET '/markdown/faqs-content.md', but there was no route defined to handle this request. Define a route for this endpoint in your routes() config. Did you forget to define a namespace?

The above happens, even though the following is included in mirage/config.js:

this.passthrough();

Presumably, this is because the API namespace is not included in the request URL.

The problem can be solved by adding the full URL to passthrough:

this.passthrough('https://localhost:4201/markdown/faqs-content.md');

Doing this has two issues:

1. I don't always know the port that the app is served on, and
2. I don't want to lose the functionality of using this.passThrough(), which automatically invokes pass through for any API requests where there is no corresponding route in mirage/config.js.

I thus have 2 questions.

1. In config.js, is there any way of getting port that Ember server is running on, to allow something like https://localhost:${port}/markdown/faqs-content.md?

2. Is there a way that I can configure Mirage to pass through for the request to https://localhost:4201/markdown/faqs-content.md, and still allow it to pass through for any other requests that don't have a corresponding route defined?