Yes, there are a few. Here is one I found once: http://webdiplomacy.net/board.php?
gameID=172577.
My team was Brazil and Argentina; to complete the lines I needed to move Newfoundland and Labrador Sea to Quebec (NC) and Newfoundland, respectively. With the right support-hold, it would have been impenetrable.
There are several ways to do it, but note that controlling Baffin Island seemed to be an important piece of the defenses up north.
This one is particularly interesting to me because you can do it with almost no control of the oceans.