ability to override a plugin's artefacts

It should be possible to override services/controllers/etc; summary of problem:

I've written a plugin, called MyPlugin.

I've written an app, called MyApp; which is designed to use MyPlugin for
base/default functionality.

MyPlugin provides a service, called ThisService.

MyApp needs to override or replace the ThisService service.

However when I try to run MyApp, or install MyPlugin into MyApp, when MyApp
has its own ThisService - I get a: "Invalid duplicate class definition of
class ThisService" exception.

This is a major hassle - to get around it I need to temporarily remove
MyApp's ThisService, then install (or) re-install MyPlugin, then remove
MyPlugin's ThisService; then finally put MyApp's ThisService back into
place so that I'm able to continue development/testing with MyApp.

More info:

http://www.nabble.com/how-to-override-a-service-provided-by-a-plugin--to15035806.html