Effectively when you sign up to an affiliate program you're promoting them, that's the point, to promote them and make some money off of their work by that single visitor you're sending them from your web site or web page; A. because you think that site is relevant and worth "voting" for, and B. that transaction ends with the single visitor from your source clicking that link (at least that's what search engines think about it).
The canonical tag actually protects their content by telling engines how best to show SERP, and yes it's also the same method you'd use to promote your site if you valued SEO.
This isn't news, I remember seeing quite a few affiliate programs that 301 their referral links and simply store the referral data in either a session or cookie or both to cover the referral... with cookies being valid for x amount of time if THAT visitor revisits.
Actually don't CCBILL program owners almost always redirect their links this way too?
This isn't a SEO trade secret. If you have a site you want promoted, you put this tag in place to verify integrity of your links. I have always thought it was common to consider your
referral ID link as SERP unfriendly and not a value worth relying on beyond the click
By the way... why don't you just build your own tour pages if you're that worried about these valuable keywords? most decent programs will allow you to do this, including if I'm not mistaken Nasty Dollars/Bang Bros etc. I know you said it was referring irrelevant terms but if someone thinks that they deserve to be above their sponsor for sponsor specific terms, you're going about it the wrong way.