Is there a way for an iPhone app to only make users download the graphics necessary for their device resolution?

I'm developing an iPhone game, and it's nearing 20MB in size. I'd like to keep it under 20MB so that users can download it over 3G.

One of the main causes is that I have two copies of all my images, one for Retina Display, and one for non-Retina Display resolutions. However, half the images are always completely unnecessary. Depending on the device it will use one resolution or the other, but never both.

I know I could just use the high-resolution set and scale them down for non-Retina Display resolutions, but they don't look as good and there are performance implications as well.

Is there any way to split my images up into two sets, and only make users download the set t开发者_高级运维hey need?

No. At least not in an Apple-supported manner.

The app bundle shall always contain everything for all platforms. One motivation: The user may have more than one iOS device synchronizing with the same iTunes library. So, say I download your app on my iPhone4, synchronize with iTunes and then also install it on my 3rd gen non-Retina iPod touch from iTunes.

Can you release two versions of the App? And then in each offer the other as a free inApp sale? Or bundle the two apps together and sell for the same price as one?