I doubt if there is anything formal. But others may know of an arrangement.
We have done several B2B's on different ships, but they were different cruise lines so I knew it was on us. When you come out of customs with your luggage, get a taxi and let them know the ship (or even better, the terminal number) you are going to board the second ship. In Fort Lauderdale, there are posted signs at the taxi stand giving a $9 flat rate to another location within the port.