How to pass through mirage request to a specific API and Host

I am using passthrough feature of mirage to allow my app to request to different API and Host.

export default function() {
  //window.server = this;
  //this.namespace = 'api';
  this.passthrough('locales/en/translation.json');
  this.get('/api/customers');
    this.passthrough();
  this.host='https://abcd.site.com';//need something like this, but not working
  this.namespace = 'api/Service.svc';

};

I want to point the requests to outside of the environment where current ember server is running. But the requests which are passing through fixed URL's like \api\authenticate.

It is throwing exceptions as follows.

POST http://localhost:4200/api/authenticate 404 (Not Found)

I want configure the requests to something like this below

http://ift.tt/2fiPIZJ

Is there any option available in ember-cli-mirage/ pretender? Please help.