class="u-in-reply-to"to the Meetable URL in my event and threw on a data tag to the front of the post like so:
<data class="p-rsvp" value="yes">I'll be hosting</data>
And of course, wouldn’t you know: it worked! The duplication of all the data on the syndicated copy disappeared, and in its place a smiling photo of me indicating that I’m attending.
Sadly, I’ve noticed that the WordPress Webmention plugin doesn’t seem to allow me to self-RSVP to my own original post within the same post. I thought I might try forcing it manually only to discover that Telegraph won’t allow the source and target to be the same URL. I also tried mention-tech which will apparently send it and report a success, but my site doesn’t seem to actually receive and display it. I will say this may be the only case I’ve run across in 5 years that I’d want to self-mention the same post and actually display the result.