facebook open graph: custom action type in post title or description
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i want to post sth. on facebook like: "Mary Run 5.5 miles with Belson". Now i've already achieved "Mery Run (action) with Belson (object)", but how chould I add the 5.5 miles? 

I tried add custom action property "distance" to "Run" and in the caption, i put {run.distance}. However, nothing shows in the attachment when i post. 
Also, i tried this: 

    FB.api(
            '/me/[app_name]:run',
            'post',
            { people: '<?php echo base_url() ?>user/'+id+'&distance=5.5'},
it doesn't work. 
I went through facebook doc, there is nothing shows how to pass data to caption or how to implement custom action property. So i'm quite confused now. Do i need to change meta tag, or is there a way to make it work? thanks