When I've done AP bookings to Africa I usually get routed through Europe and Asia is not an option as a stopover because it is past the turnaround point. You may need to try and piece something together or better yet, call into the call centre and see if there is any creative way to make it happen. Generally any itinerary I want with stopovers that is the easiest - or look at two one-way segments but check on the prices of a ticket for the Africa-Asia transfer first.