No, it’s not possible indeed. I never manually check-in. I either scribble from Plex (rarely, to be honest), or I do a manual check-in upon finish watching an episode or movie.
However, if you are on either the Google Chrome or Firefox browser, there’s this neat little add-on which I mentioned in another thread. If I remember correctly, it also scrabbles from your browser! (It doesn’t however work if you’re watching from a smartphone or smart TV application, because obvious reasons).