I normally don't like to launch a feature that's this rough around the edges, but I decided to anyway. I added a section to the OwnYourSwarm dashboard that will let you import a specific checkin by its Foursquare checkin ID.
When you click "Import", the processing flow for that checkin is started in the background. There is unfortunately no feedback in the UI on its progress yet, but in a couple of seconds you should see the checkin appear at your website. Shortly after, any coins, likes, and comments are sent via Webmention as well.
This is mostly laying the groundwork for adding the ability to backfill checkins that were made via the "offline" checkin feature, as well as the ability to do a mass import of your checkin history.
In the mean time, you can at least enter a checkin ID manually to trigger an import if any were missed because they were "offline" checkins.
nice! and great precedent and example for the corresponding bridgy feature request. much appreciated.