Ember v. 2.x: watch vendor folder

I'm developing an Ember-JS application with a lot of JavaScript that performs of all kind of UX and styling tasks.

Because these tasks fall out of the scope the MVC-logic, I've put them into modules that I put in the vendor map.

Putting them into the Vendor folder doesn't mean I'm done tweaking these files, but to test them, I'm required to re-start the ember-server over and over again.

How can I make Ember watch these JS-files in my vendor folder and re-compile them when I change them?

The following page answers for Ember v. 1, but doesn't apply to Ember 2.0: http://ift.tt/2kwU4RS

I also tried creating an addon, but ember (cli) answers with: “You cannot use the addon command inside an ember-cli project.”