I'm interested in a mixed class fare on my forthcoming trip to SE asia (something like Business class from LHR to HKG and economy from SIN to LHR).

I phoned Etihad and they said you can booked mixed class fares on their web site. This has also been stated on a trip advisor thread. Problem is it's not obvious on their site how to do it (as opposed to Emirates where it is easy).

Has anyone ever made a mixed class booking on the web site. If so, how?