Injector::get will create the object for you, which you can then customise using  config or `Injector::inst()->load($config)`.  you should probably name your service after the interface and have a default YML that maps the default class.

I think the below will do it...

```yaml
Injector:
  Cookie_Backend: '%$CookieJar'
```

and then `Injector::get('Cookie_Backend');`