Nauti Nymph and a few other companies will rent you a boat w/o a Capt if you can demonstrate a reasonable level of boating competence - really the only reason to obtain a Captains License from the USCG is to carry Passengers for Hire - working as a paid Captain or boat owner ------ it is expensive to acquire and even more expensive to maintain, unreasonably so, if you are not a working Captain and have the initial sea time to qualify.
It will be extra hard to convince a rental company to rent you a vessel for 'a few days' - they will not want you operating after dark and there are VERY few places in STJ to keep the vessel safely or legally overnight. Give it back to them at the end of the day and tell them when you need it in the morning - why have 24 hr. responsibility anyway??
[altouchet] - I would think you would easily qualify to rent a boat from any rental company here with your experience and a bit of chart reading demonstration.
You don't need the boat after sunset or before sunrise why pay for the vessel responsibility ?