Hypothetical Situation: I have a small obscure website called "miniatureBoltsInCarburetors.com" which provides content about the miniature bolts which hold a carburetor together as well as some general related automotive information. My site also has a single page which allows someone to find the missing bolt in their carburetor, and while no one will access this page directly from my website, one billion other popular automotive sites have embedded this single page in their website using an iframe, yet not included a link back to my site.
I recognize that this question is related to SEO which is considered off topic, however, all of the many SEO related forums discuss the marketing steps one could take, and not the programming steps or strategies, and hope others will allow this question to be answered here.
I wish my site "miniatureBoltsInCarburetors.com" to be ranked high for general automotive searches. What could I do to allow the 3rd party sites which include an iframe back to my site to improve my ranking? Could using JavaScript in the iframe to create a link on the parent page provide any value? What about when my server renders the page, use PHP to get the referring URL from $_SERVER, and include it in the content?