I'm trying to inject the og protocol meta tags to my dnn (5.6) page header.  The example on the facebook site is something like:-

<meta property="og:title" content="The Rock"/> 
<meta property="og:type" content="movie"/> 
<meta property="og:url" content="http://www.imdb.com/title/tt0117500/"/> 
<meta property="og:image" content="http://ia.media-imdb.com/rock.jpg"/> 
<meta property="og:site_name" content="IMDb"/> 
<meta property="fb:admins" content="USER_ID"/> 
<meta property="og:description" content="A group of U.S. Marines, under command of a renegade general, take over Alcatraz and threaten San Francisco Bay with biological weapons."/>

If I paste my version of the above into the Page Header Tag in Page Settings, it gets unceremoniously truncated at 500 characters,l which just aint enough (and breaks the page unless you spot it!).

Is there another easy way to inject the above into the header?  It needs to be different for each page, so editing default is not a solution.