Não tenho certeza de como o oneboxing está configurado para posts de blog no Discourse

[Alexander (Alexander Barrios)]

Você quer dizer a mensagem que diz “Originalmente postado em…”?

Embed Discourse comments on another website via Javascript

Discourse has the ability to embed the comments from a topic in a remote site using a Javascript API that creates an IFRAME. For an example of this in action, check out Coding Horror’s blog. The blog is run via Ghost but the comments are embedded from his Discourse forum. One important thing to note with this setup is that users have to navigate to your forum to post replies. This is intentional, as we feel that the posting interface on a Discourse forum is currently much richer than what we …

Não tenho certeza, mas acho que é isso que você está procurando.