Open Graph Markup in Blocs

We need an easy means of adding code into the HTML tag for use with Open Graph, to get certain images to display when a URL is posted in FaceBook, for example:

<html prefix="og: http://ogp.me/ns#">

We just need to add that Open Graph code in either the HTML or HEAD tags and then add other OG code which links to the image we want to display in FaceBook.

I don’t want to hand-hack page code every single time I export from Blocs, which is why Blocs need a built-in solution for this.

Thanks.