I have a website that uses the Group Buying Site plugin (http://groupbuyingsite.com). It uses facebook app to login and register.
When I add a new item to the cart the user is redirected to
Assuming you have the access token, I suggest you try this:
$result = $facebook->api( '/me/feed/', 'post', array('access_token' => $access_token, 'message' => 'Your Post here') );