Except a special-case of transclusion: high latency and compile-time only. As opposed to doing it with JS dynamically; if Pinboard had an API, or even simply doesn't block frames with HTTP headers, you could simply dynamically call from the static site page to the other site, load the relevant HTML, and present it transcluded into the static site page. (This is how Gwern.net does a lot of stuff: everything from the Wikipedia/Github popups to transcluding other pages.)
Except a special-case of transclusion: high latency and compile-time only. As opposed to doing it with JS dynamically; if Pinboard had an API, or even simply doesn't block frames with HTTP headers, you could simply dynamically call from the static site page to the other site, load the relevant HTML, and present it transcluded into the static site page. (This is how Gwern.net does a lot of stuff: everything from the Wikipedia/Github popups to transcluding other pages.)