You do not specify type, but I would agree with dhardesthard post #9.
2 questions:
Is your scenario pre-EDTO entry? In which case I would have thought you were not EDTO 'capable'?
If post-EDTO entry, would you not require the APU running anyway for EDTO (twin assumed) in which case I would have thought the extra fuel would be pretty much negligible? There is always load-shedding to be had as well.