Amazon may make it difficult but I cannot see that they will remove the functionality completely. Many people are buying the fire stick to be able to view Kodi. if they prevent them from doing so they will be reducing Firestick sales themselves.
This with bells on. I purchased the below box via Amazon and set up with the excellent instructions provided on the thread. Works a treat
https://www.amazon.co.uk/gp/product/B019XCW9ZO/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1