I would visit the concierge on the first day as they can fill up quick. I don't think it's possible to book in advance.
11 cruises in 2012 finished!
Total: 90nights at sea visiting 15 countries
BOOKED: Princess Diamond May 25th for 28nights to Alaska
PM me if you need a cruisemate for any Panama Canal cruises in 2013
Celebrity preferred but not required
Date, ship, cost pp