Ember, how to inherit from a custom Adapter

I have a global custom Adapter:

// app/adapters/application.js
import ActiveModelAdapter from 'active-model-adapter';

export default ActiveModelAdapter.extend({
  namespace: 'api',
  host: 'http://ift.tt/1SbiS8C'
});

And another specific for one Model:

// app/adapters/chart.js
import ActiveModelAdapter from 'active-model-adapter';

export default ActiveModelAdapter.extend({
  namespace: 'api',
  host: 'http://ift.tt/1SbiS8C',
  buildURL: function(type, id, snapshot) {
    return this.host + '/' + this.namespace + '/reports/' + snapshot.record.get('report.id') + '/charts/' + id;
  }
});

As you can see there is a duplication defining the attributes 'namespace' and 'api'. This is one of the reasons I'm trying to inherit the ChartsAdapter from the ApplicationAdapter.