My concern about a dinghy is that getting it out of the aircraft is not going to be easy. But, if you have one, and get it out - you are much better placed.
The insurance is not interested in multiple pilots - they are only interested in the qualifications/experience of the PIC.
Good luck with finding a freebie trans-atlantic flight - join the queue!
If, though, you are prepared to pay a share of the costs then you might find someone who will want you along for the ride!
Safe flights, Sam.