Hey Tikka,
Yes, you can get right next to the ship, within shouting distance from the open decks. The ship docks in such a way that the bow of QE2 points due east into Manhattan, and the port side is aligned with a quite a tall wharf building capped by a car park. When I have arrived into/sailed from New York before, there have been plenty of folks who have been on what seems to be the roof top car park for whatever building it is, chatting with and waving to people on the ship. The level of the car park/roof of the building is broadly the same as the outside decks of QE2. Whether access to that building and its roof/car park is more restricted now than in the past, I'm not sure.
I will next be on board this coming Saturday, May 18 and sailing into New York to arrive May 24 (the day your friends depart). And I'm looking forward to a hard earned rest on board! Anyhow, I called Cunard and asked for some guest passes to have friends come on board at Southampton for a bon voyage party. Cunard has always been very willing in the past to grant these requests, although I have been told both by my agent and by Cunard directly that post 9/11, only bona fied passengers and crew are permitted on board. Such a shame.
Cheers,
Ed