Including a non-bower dependency in an Ember CLI Addon

I'm creating an Ember CLI Addon for a plugin that isn't a registered Bower package. Normally when creating an addon you'd put the bower package in bower.json and then include it in the afterInstall hook like this:

afterInstall: function(options) {
  return this.addBowerPackageToProject('path/to/bower/package.js');
}

So if it's not a bower package, do I just download the script and import it in Brocfile.js the same way I normally would in an Ember project? Is there a better/preferred way to do this?

Thanks in advance. Also in case anyone asks, the plugin is for a BookBlock component.