I can't answer your question directly but when the fuel filler lock on my mums metro played up I dismantled it and removed all the tabs to make it possible to unlock it with any key of the correct profile. With that in mind it may be possible to modify the barrel with the tabs from the door lock.
Home to black Alfa Romeo 159 3.2 V6 Q4 ,green MGF VVC and red MG Maestro T16.
MG - the friendly marque.