I have an issue.

I need to a make a flight to New York to personally pick up something, sign some legal stuff, etc.

I have found it's quite a bit cheaper to fly from PVG-JFK/EWR vs booking directly from HKG-JFK/EWR.

I have a flight that's flying from HKG to PVG I plan to just not fly, so I don't have to fly from HKG-PVG only to fly right back to HKG immediately to fly to New York.

If I book the PVG-HKG-EWR/JFK-HKG-PVG flight, can I somehow get them to void the first segment after booking without canceling my whole ticket? Of course to save money I am willing to do the roundtrip in Shanghai, but I want to avoid it.