Multiple Android Application Package .apk files from single source code

I’m generating 2 different APK’s (demo and production) from one single source tree with 3 small modifications:

1) I have public static final DEMO=true; //false; in my Application class and depending on that value I used to switch code between demo/production features

2) There are 2 main activities, like:

package mypackage;
public class MyProduction extends Activity 
{
    //blah-blah
}

package mypackage.demo;
public class MyDemoActivity extends mypackage.MyProductionActivity
{
    //blah-blah
}

3) And in the end 2 separate AndroidManifest.xml files which points to different launcher activities depending on demo/production switch

I’m switching between 2 APK’s manually, but see nothing difficult in writing small ANT task to switch between them automatically