I just loaded the kobo reader to my Fire. Here's what I did...
1) Install the
Box app on your Kindle.
2) Download the
Kobo apk to your PC.
3) Logon to
Box from your PC and upload the Kobo apk.
4) Open the Box app on your fire, logon, and open the apk
5) Install the apk
6) Open Kobo, logon to your account, and get your books.