I own an Onyx Poke and I buy my books at kobo. They work just fine. With a jailbroken Kindle capable of processing EPUB this should (!) work. Give it a try with

I own an Onyx Poke and I buy my books at kobo. They work just fine. With a jailbroken Kindle capable of processing EPUB this should (!) work. Give it a try with an inexpensive book, maybe?