The USB interface is a feature that's tied into the head unit, it can't simply be a exchange of the plug. Now changing the whole head unit out and the aux in certainly looks like it will fit (why not, similar dash), I don't know about the harnesses though.

It seemed like an easy enough feature to implement, since the radio was always designed to decode lossily compressed audio, although intially from optical media only. Now it's just doing the same thing from a different medium.