Assuming appended itinerary complies with 2 stopover 2 transit one open jaw rule
And assuming you did not take any QF (or otherwise non-CX/KA) metal in the whole itinerary

Yes possible
You still need 2x one-way mileage in your account for CX to issue two one-ways
And you will pay taxes and surcharges as if two one-ways.
But the mileage difference will be refunded on application after conclusion of your journey.