Product Variations - how to offer both physical product & digital download?

I'm trying to offer both an audio CD and an mp3 download as product variations in MarketPress, but can't figure out how. First off, if I offer a download, I can't add any variations. And if I could list both "Audio CD" and "MP3 Download" as variations, there's no way I can see to link the download to the MP3 variation. Am I missing something, or is there perhaps a clever workaround anyone's figured out?

As it stands, seems like I'll have to create separate product listings for the CD and the MP3, which is less than ideal...

Thanks!