Facebook doesn’t support this. Facebook only supports plain texts, so the plugin strips all markup.
Why can’t the plugin strip all text after the divider before posting over to FB?
So – why can’t it be an option? I ask because of this:
Not working like you think it should defeats another feature – the ability to choose whether or not to post a youtube video to facebook. The “don’t post video to FB” option is great because it makes sense because people would naturally check that box in order to drive traffic back to their blog to watch the video.
Example post:
Type in intro sentence, place the “more” divider, embed the video below, and post more text under the video.
Facebook grabs all of this including the video link and posts to facebook. Users then see a perfectly-formed youtube link and can go right there, skipping the blog post completely. The only way to get around this issue is to make a lot of intro text so that the character count cuts it off.
This plugin exists for over three years and nobody asked for this feature ever before, so IMHO this is not a feature that is worth the effort to implement.
If you want, you can contribute this feature. Just send me a diff file of the changes after you have tested the change thoroughly and I will apply the changes to the next version.