J.S if you have the QFE option simply use it if you go to the places where altitude instructions below TL are given by the reference to QFE. No brainer there. Airbus is gonna take care of the rest. Obviously you'll need to use DH and associated approach procedures. If you elect to use QNH with QFE based altitudes then simply add the field elevation to any given height to obtain the altitude
Careful on that. The EGPWS database in Boeings isusually based on AMSL and assumes QNH unless the aircraft is equipped accordingly.
Is the Airbus different?