The simple solution is to stop buying eBooks from Amazon. Pirate all of your epubs and PDFs so you will always have an offline backup. If you enjoyed the book buy a hard copy for a friend, relative, book club, etc from a local book store. Amazon doesn't need your money anymore.
Your solution hurts authors more than Amazon. Just buy ebooks from somewhere else! Don’t be cheap and pretend it’s principled. I know you say buy a copy if you enjoyed it but that’s not really how commerce works and none of these authors agreed to offer you donationware.
Personally I'm glad to pay for a book later if author provides alternate method for payment. But to pay for the book just to flip trough it and decide it's not for me is not worth it.