Actually, the best practice for Ensemble is now to subclass %CSP.REST directly and call the Ens.Director.CreateBusinessService() method to instantiate the class as a business service. The next revision of the Ensemble documentation will have the following note:
Although Ensemble defines a class EnsLib.REST.Service, that is a subclass of %CSP.REST, we recommend that you not use this class because it provides an incomplete implementation of %CSP.REST. The only feature that EnsLib.REST.Service provides that is not available from %CSP.REST is the ability to use a special port, but we recommend against using a special port because it does not provide the robustness and security you get by using a commercial web server and the CSP port.
If you just want to pass through a REST call to a REST business operation, you can use EnsLib.REST.GenericService.
The ENSDEMO Demo.ZenService.Zen.WeatherReportForm.cls demonstrates how to use CreateBusinessService with Zen not REST, but the use of CreateBusinessService is the same.