In the case of EWR-HKG, there are no P fare filings at all. Even if there is P bucket available, there's no P fare to go with it and the lowest you can get is a Z fare. However, UA does have P fare filings for PHL-HKG route and fares are as low as $4K roundtrip from there (your ZFV trick also works), so OP might want to consider flying from there.
Thanks for the tip - I checked out those fares and for my dates it seems takes three flights in each direction to get the P fare (i.e. PHL-IAD-ORD-HKG / HKG-SFO-ORD-PHL) but it is cheaper -- and then I end up back in PHL.... I guess I might have to go to another airline for this trip....