As far as I know they took it all away when 9/11 security was implemented.
However, I have tipped curbside checkin baggage handlers outdoors to hold luggage for me before. Just be absolutely sure they understand what you are asking, and set the timeframe for when you will be back. Don't leave anything valuable.
Why not check in to your flight then you don't have to worry about your luggage or check in when it is time to go.
Or if your cruise line offers a "luggage express" service it could be well worth two trips to SJU.
All I ask is a tall ship and a star to steer her by; John Masefield
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014, 2016
Sail Windjammer: Mandalay 2017
Star Clippers: Royal Clipper 2015