I think if you use the actual database field names, it will work; the documentation says do this:
orderby=rating,id
It doesn’t work, but this does:
orderby=rating,link_id
The database field names are (in version 2.9.2) are:
link_id
link_url
link_name
link_image
link_target
link_description
link_visible
link_owner
link_rating
link_updated
link_rel
link_notes
link_rss