Android :: How To Factor Code For Free / Paid App Versions?

I have a project which I want to split into a paid and a free version. I do not care to double my management of the res/ folder and would even like the Android Manifest.xml to be the same file except for the package line. Worrying little about hacking (at this stage - my app is not copy protected anyhow so other avenues of vulnerability are already open), it might be sufficient for me to have all the logic in the free app, and to enable/disable functions based on the app's own package info. What strategies have others used in this regard? I have soft-linked the source from a new Android Eclipse project folder tree to the existing one (the new is to become the paid version and the old one will become the free one with some logic paths being conditionally stubbed at runtime), reserving the new source file hierarchy in the new one to the sole purpose of containing an My Main Activity.java file (as it will need to be in a different package- folder than the one for the free app's). But the res folder appears as though it might be more difficult.