It appears that you have to extract the URLs of the actual swf in the page and the thumbnail image yourself. For example, this seems to work:
curl -F 'access_token=...' \
-F 'message=Link to YouTube' \
-F 'link=http://www.youtube.com/watch?v=3aICB2mUu2k' \
-F 'source=http://www.youtube.com/v/3aICB2mUu2k' \
-F 'picture=http://img.youtube.com/vi/3aICB2mUu2k/0.jpg' \
https://graph.facebook.com/me/feed
It appears that you can generate a valid source and picture from the page URL. The URL looks like http://www.youtube.com/watch?v=<code>; take the code (3aICB2mUu2k here) and insert it into the URLs http://www.youtube.com/e/<code> for the source and and http://img.youtube.com/vi/<code>/0.jpg for the picture.