Multiple Versions of the Same Android App

I've been researching online for the past few days on different methodologies to manage multiple versions of the same android app. I'm planning to release a paid version for Binary Calc with extra features. The truth? Two and a half weeks later, I realized ads aren't enough to generate $moola. I need to buy my next high end android phone. Thus, I have resorted to paid apps. At least I'm honest.

I've considered creating additional project libraries and using my app as the core library, but this proved to be quite tedious. There's the Touiteur way, create a separate paid app and use that as a "key" to unlock features in the free app. I've settled on just manually renaming the package name when the time comes to export the app. In Eclipse, a search and replace (Ctrl-H) works like a charm. There's always the fancy way of using an antlib task too.

Edit:

Specifically, to do it my way, you would:

1) rename the main package and make sure to check "rename subpackages"

2) do a search and replace of the package name to catch any stragglers

3) rename app_name if necessary