I found a solution to this by adding the images to the body and not in the meta information, then just hiding them, like this;
...
etc
...
It just came to me from reading that if no og:image property is given then thumbnails are taken from the body, and it worked even if hidden. You could probably remove the width, heigh etc to tidy it up, but I thought why both waste time with that when it gets hidden anyway, I just cut and paste and made it hidden.
Hope this helps.
