Support for custom album cover/online store modules has been implemented for v3.
Meantime, the only way to do it would be to implement your own solution externally... you could hook into the existing JSON API used by the Recent Tracks widget to get the recent tracks list (or use the XML API to do this), then parse the song titles to find the tracks in your store.
The XML API is documented in the SDK (available for download in your client area). The JSON APIs used by the widgets are considered to be internal and are not documented, but if your developer is reasonably experienced they're pretty straightforward to figure out.