I "tried" to jumpseat on Spirit to FLL from PUJ about three years ago. The agents weren't too sure how to go about it, and then finally said it wasn't available. All was not lost though as they sold me an ID 90 (around $80) and gave me a first class seat for the flight. I went to say hello to the flightcrew and they said I was ALWAYS welcome on their jumpseat and that they wished they'd have known I was trying to catch a ride. It all turned out great though and the crewmembers were fantastic.