Which apps are you talking about? If they were preinstalled on the G2 but not the G4, that will be difficult. You could try searching for the apk installer files on the web, but even if you found them, they probably wouldn't be compatible with the phone.
There's an app called "APK Extractor" that will copy an app APK file to local or SD storage on the phone. Install it on the G2 and extract the APK of the app you want. Upload it to dropbox, then download and install it on the G4. Whether it works or not is another question.