Earning unlimited amount of steem for a single post may not be possible as you think because the steem blockchain is programed in such a way that you have only 7 days to earn any amount of steem for that same post and once it exceed 7 days, it is over which gives you a chance to redeem your earned steem or SBD into your Steemit wallet. I actually read an article online by a whale who states that there are times whereby the payment may exceed 7 days provided the article or post is very controversial when it makes it to the trending page. I actually don't know how real this is since I haven't experienced such before.
I think if you really want to earn more steem for a particular post, i will suggest you break or divide the particular topic into different numbers. This is mostly adopted when you are writing about story or making #ulogs posts about yourself or when you take part in #contest like #30dayschallenge. This method involves you starting from Day1 or 1 to the number of days you are capable of stopping. I think this can actually earn you more steem for that particular post title.
You can also earn more money with your Steemit post by making use of other platforms which support your posts. You gave an example of earning through Amazon and that's actually one of the ways to go about it. When doing this, you just have to be careful of plagiarism because Steemit is very strict when it comes to plagiarizing people's content.
In conclusion, if you really want to earn unlimited steem, you have to keep making unlimited quality content on the steem blockchain.
Thanks for reading and I hope this helps.
What is stated in the other comment is not necessarily true. There is a way to make extend the time your post can earn rewards.
The people behind Steem-Bounty created the 'Steem Forever'-tool. This tool allows you to convert the link to your SteemIt post into a steem-forever link. When people visit your post through that link, they can give you an upvote and you will receive rewards... even when a posts is 2 years old.
You can read more about Steem Forever in the intro post:
You can find a similar service on https://beempy.com/rewarding - but I'm not very familiar with it.
Tips can be given out using the @tipu service. They've just changed their ways and are now working with a token powered by Steem-Engine.
Read more here:
You can also add a Likecoin button to your posts. I wrote a post about it a couple of days ago
Idk about link shorteners. The community didn't like them in the past. But then again, they didn't like affiliate links either. When I just started out,I got flagged down to rep 11 for using affiliate links. But now, they are all over the place.
Still, I don't know if things have changed in the same way regarding link shorteners. After so many people got hacked last year, everyone became more cautious with links, especially shortened links.