Dream 747, actually your question is relevant here:
It is not the same to have two engines inoperative and no APU than two engines inoperative with the APU running. The latter is much less stressing for the crew, to say the least.
So, with APU running, the question remains: Y ELEC PUMP, yes or no?
If the Airbus engineers don't use it in the procedure, it is because something could be not OK with that. There's a few things to consider: The output power of the Y ELEC is very limited, it seems.
If I was to use it, I would turn the PTU OFF first, so the elec pump wouldn't also have to power the green system. Then I would turn the Y ELEC ON and use it: Conf 3, then turn it off again.
As an added thought, APU ON take offs could could become standard procedure when there are birds in the airfield.