I am flying from Tunis to Hong Kong via Dubai in December. Last year, I got those upgrade offers via email, one for each leg: TUN-DXB, DXB-HKG, HKG-DXB, DXB-TUN.

I would like upgrade for cash without waiting for the offers but the EK website does not let me upgrade for a single leg but force me to upgrade for the whole sector (i.e TUN-HKG or HKG-TUN). Does anyone know how I can upgrade to the night flights only (DXB-HKG and HKG-DXB)?