I think I'm looking for the same thing. I have a kindle paperwhite and the kindle app on my lumia 920. I use the send to kindle button in chrome, or otherwise email documents to myself, and this works great on the paperwhite. But if I go to the kindle app on my phone, it only has the official kindle-store books. My articles and documents are not making it to the WP8 kindle app. Is there a setting I need to change or something? Or is this just the same old story where the WP8 app doesn't have all the features of the ios/android apps?
EDIT: I just re-read his post and I'm looking for a slightly different thing. Still relevant though.