How to change og meta for homepage?

I know you posted this four months ago, but just in case you’re still wondering (or someone else stumbled across this site) here’s how I solved the issue for one site:

I altered the plugin code in wp-content/plugins/wp-open-graph-meta/wp-open-graph-meta.php. I changed the function add_elements() from this:

public function add_elements()
    {
        if (is_singular()) {
            the_post();

            $this->_metas['og:title'] = $this->_get_title();
            $this->_metas['og:type'] = is_single() ? 'article' : 'website';
            $this->_metas['og:url'] = get_permalink();

            $this->_metas['og:description'] = $this->_get_description();
            $this->_metas['og:site_name'] = strip_tags(get_bloginfo('name'));
            $this->_metas['og:locale'] = strtolower(str_replace('-', '_', get_bloginfo('language')));

            $this->_add_image();
            $this->_add_post_tags();

            $this->_output();

            rewind_posts();
        }
    }

To be this:

public function add_elements()
    {
        if (is_singular()) {
            the_post();

            $this->_metas['og:title'] = $this->_get_title();
            $this->_metas['og:type'] = is_single() ? 'article' : 'website';
            $this->_metas['og:url'] = get_permalink();

            $this->_metas['og:description'] = $this->_get_description();
            $this->_metas['og:site_name'] = strip_tags(get_bloginfo('name'));
            $this->_metas['og:locale'] = strtolower(str_replace('-', '_', get_bloginfo('language')));

            $this->_add_image();
            $this->_add_post_tags();

            $this->_output();

            rewind_posts();
        }
        elseif ( is_home() )  // Added by @tommygeorge:
        {
            $this->_metas['og:title'] = strip_tags(get_bloginfo('name'));
            $this->_metas['og:type'] = 'website';
            $this->_metas['og:url'] = home_url();

            $this->_metas['og:description'] = strip_tags(get_bloginfo('description'));
            $this->_metas['og:site_name'] = strip_tags(get_bloginfo('name'));
            $this->_metas['og:locale'] = strtolower(str_replace('-', '_', get_bloginfo('language')));

            $this->_output();
        }
    }

As you should be able to see, I simply added an elseif condition, and altered the tags I wanted to show up on the front page. It may need further modification to be more friendly with some SEO plugins, or to work properly with a static-page front page. This currently works with a front page that shows posts.