You could fly from PEK to HKG and then connect to either CX's non-stop flight to JFK (leaves around 10 AM, arrives around 2 PM) or CX's afternoon departure to LAX (leaves around 1 PM, arrives around 10 AM).
You'd probably have to overnight in HKG, though.
BA's and VS' flight from PVG to LHR leave in the late morning and arrive in the evening. Not sure if they arrive too late to catch the last flights to JFK, but I suspect they do.