There were a few patches that attempted to improve upon the built in piano. You've probably seen them all in the libraries. None ever satisfied me. This is where you turn to an external module. Can you send midi into the iPhone for your piano app and play it from the VFX keyboard? (I've used the camera connection kit and a USB midi interface to play Arturia's iMini - minimoog emulator - on an iPad, so it's not as far-fetched as it might sound.)