If you feel like a road trip, La Parguera on the SW coast offers some offshore kiting around the mangrove cays.
http://www.fksa.org/showthread.php?t=848
For a current contact for sea taxi to the riding area and other spots in PR checkout:
http://www.prkbc.com/
There are some challenging wave venues north of Mayaguez, the link above should be able to fill you in on prospects.
p.s. - what Raul said, if someone says they're going to kill you, take it seriously!