All you have to do is get a hold of two apk's com.amazon.kindlefs and samsungservice
I got the first one by searching Google and someone posted a link to it in a comments section (I lost the link though so you will have to find it)
You should also be able to extract it from a stock based phone that got it the right way from "Samsung Apps"
Then for it to work right and let you get the free book you also need the "Samsung Account" app which is just samsungservice.apk. Easy to get from any rom or search xda I found the apk it self without having to download a full rom.
Installing both of those was enough and I got my first book free.