Introduce momentary delays in ember-cli-mirage

I am using ember-cli-mirage for acceptance tests. For a specific case, I would like to check the behaviour while fetching data over a slow connection.

There's a setting in ember-cli-mirage called timing that simulates a delay in the response. However, this setting cannot be changed to be different in a specific test:

// app/mirage/config.js
this.timing = 400;

Something else I have tried is returning a promise at the fake endpoint. Through some import/export, I could control the resolution of the promise from my test. Unfortunately, ember-cli-mirage doesn't seem to recognise the return value as a promise, and simply passes it back to the adapter verbatim:

// app/mirage/config.js
this.get('/StopPoint/Search/:term', (db, request) => {
  return freezer.run(function() {
    return db[`stop-point-search-${request.params.term}`][0];
  });
});

// At my test
freezer.on()
runTests()
freezer.off()

The question: is there any way to do this? Ie: to control the delay of a specific response in ember-cli-mirage?