Ember Engines inside Rails Engines via ember-cli-rails

We have a high modular rails5 app, which is splitted in rails engines over serveral repositories and integrated as ruby gems.

Now we want to introduce EmberJS by using ember-cli-rails. The main rails application contains the main ember application in the frontend directory while each of the rails engines contain an ember engine (via ember-engine) in a frontend directory.

How to mount the ember engines of the modules into the main ember engine?