PreferenceActivity with multiple preference files

The way to use a preference file (instead of the default shared preferences) in PreferenceActivity is as follows:

public class MyPreferencesActivity extends PreferenceActivity {
    protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);

         PreferenceManager prefMgr = getPreferenceManager();
         prefMgr.setSharedPreferencesName("my_preferences");
         prefMgr.setSharedPreferencesMode(MODE_WORLD_READABLE);

         addPreferencesFromResource(R.xml.preferences);
    }
}

In this example we use the Shared Preference named "my_preferences". But how would we use more than one custom preference in the same PreferenceActivity?