That's an excellent question. Unfortunately, we don't currently have support for that button, but I like the idea. We should be able to add that to our existing JReviews plugin and it *may* be possible to create a custom action to do that now (it will just be a little more work than if it's in our JReviews Open Graph plugin).
Can you let me know what version of JReviews you're using? We have v2.4 on our development site and have some good things planned for JReviews, but I just want to make sure we're researching the right version for you.
Thanks,
Alex