If you put the live and test versions of the extension point implementation in different plugins you can then choose which plugins to include in the product build - so you would have two product configurations, one for testing and one for production. When you are testing in Eclipse you can configure the plugins to include in the Run Configuration, so again you would have a test and production configuration.
It might also be possible to use a plugin fragment to contain just the part which varies. Use New / Project / Plug-in Development / Fragment Project to create.