I do not know if my post is still relevant as you discussed quite a lot.
Any way, here is my "contribution"
Without access to the database and without creating an autoindex job to process all the database to copy the system DOCID to a custom DOCID, I found that searching the DOCID using the fulltext gives pretty good result.
Sometimes it might return more than one document as the DOCID number can also be a value in a document.
Of course this is fully manual, a little but quick and dirty, but it can help