You can mix any of those.

In theory the rule is that the open leg, e.g. PEK-HKG, has to be shorter than each of the flown legs, e.g. LHR-PEK & HKG-LHR. So any Far East combination will be fine. In practice they don't seem to enforce this consistently anyway.

There are also OW flights to MNL from KUL and TYO if that's helpful. And the 72hr PEK transit rules may help.^