Reading the responses, I agree the beleaguered garrison makes the most sense.
So now that the season has passed, this is the situation that raised this seemingly absurd question. Look at the board position going into autumn 06: http://webdiplomacy.net/board.php?
gameID=203429I (France) can attack Edit from Lvp or Nth. So if Russia is working with England to defend, suppose he uses Hel S Edi-Nth to block the attack from Nth, and also Nwy & Den S Nwg-Nth to a) cut support, b) Prevent Edi from actually succeeding to Nth and c) Attempt to capture Nth. This blocks both obvious attacks on Edi.
So I considered the clever attack of Lon & ECh S Edi-Nth while Nth flees somewhere. This allows Lvp to walk into Edi *if* the season plays out as expected. I was hoping to also use Nth to cut Helgo just in case he attacked Holland (which he did) but didn't want that to prevent England from succeeding to Nth.
In the end England didn't submit orders so it all came to nothing but I was just curious how it would have played out.