Imagination running wild, what about the other way around? Trent XBW for the dugong, enabling a stretch. The redesigned fuselage comes with a reinforced floor for the cargo variant (where volume matters), and the cockpit is pushed upwards(*) to allow for nose-loading door. Bleedless installation.
(*) or somewhere else completely, synthetic vision permitting.
Oh, sorry, this thread is saving the engines not the skeleton.
Sounds like a new aircraft anyway.
(exits stage through the trap-door)