On an existing circuit, or on a new circuit with a new breaker?
If on an existing circuit, start from the front GFCI outlet between the driver's seat and the galley. Trace it backwards until you get to the panel below the rear driver's side cup holder. Remove the cup holder to provide access.
Carefully cut out your opening for the new outlet; you've got wires and plumbing behind that panel and cutting either one by accident would be bad. Cut the wires leading to the front outlet. Wire both cut ends into the new outlet so that the circuit still runs to the front outlet from the new outlet. Insert the outlet in the hole you cut and secure it in place. Reinstall the cup holder. Done.
Adding the outlet doesn't add to your capacity; you're still limited to 15 amps on any one circuit, and 30 amps total for the whole 120vAC system. It would be a good idea not to use the front outlet while you're using the new rear outlet.
Caveat; do not add another GFCI outlet to a circuit that already has a GFCI outlet, unless you like so-called "nuisance tripping." Install an non-GFCI outlet instead. Circuits that need more than one GFCI outlet should have a GFCI breaker instead, and no separate GFCI outlets.
Engineering: Finding complex solutions to simple problems you didn't even know you had.