my trip will be TPE and HKG, hence, I can't do YYZ-HKG-TPE {stop} TPE-HKG {stop} HKG-YYZ.
Why not? I have exactly this on an AE reward- stop in TPE en route to final destination, then transit TPE on the way back.
Right now I am on a ticket on which I transited SIN a while back, and
tomorrow I am stopping there for a while.
You might have to phone it in, but it can be done.