Multi city booking - different fare types

[Stuser]

I want to make a “multi-city” booking with Singapore Airlines, flying Perth - Singapore - Bangkok
Returning BKK - Sin - Sydney

I’d like to fly economy Perth to Bangkok
And Premium Economy back, but the website tells me because it’s “multi city oh no so difficult” that my fare buckets have to be the same (!)….

So does anyone know or have a workaround?

 

[wenglock.mok]

The website doesn't seem to allow this using the multi-city tool so you might need to get an agent on the phone to help you.

The fares are definitely combinable "on a half round-trip basis" so what that means is you can combine half of a roundtrip Y fare PER-SIN-BKK and half of a roundtrip W fare BKK-SIN-SYD.