I would guess off season for most Americans to Central America would be rainy season. That is probably off season for most travellers. You might be able to travel between Thanksgiving and Christmas but I would guess that mid Dec. (going to C.A.) though the beginning of January (returning) will be busy due to the holidays. Remember its winter here and people want to travel where it is warm.

Also, you need to check with your company. My company has not allowed us to let travel partners use myidtravel. When I look Jetblue does not even show they allow travel partners but icelandic are does. What about airomexico? it shows travel partner and that might get you somewhere into Mexico.

Also, what about a Canadian airline, you have any options there?