For power push you need NWS to steer the airplane, so in old models you need green hydraulic power. You could get green pressure by means of the PTU with the yellow elec, if both engine master switches are in off or on, according to the logic. But as soon as you started one engine, the NWS would be lost and power push impossible, wasn't it for the fact that PARK BRK OFF and NWS NOT IN TOWING POSITION is a condition where PTU works, as well.
On ground, engines off, with parking brake released and without the pin bypassing the NWS (no NW STRG DISC memo), PTU will operate as soon as the yellow system is pressurized (when number 2 is running). Then you can initiate power push. I think the elec pump is not used for the procedure, you just start number 2 before starting the push.
I've never done this powerpush myself