About 4 years ago I was able to use BA miles to fly myself & Mrs hbr245b JFK-LAX-SYD-MEL in business class on QF; on the return we flew SYD-AKL-LAX also via BA miles in business class on QF.

We had semi-fixed dates as we were attending a wedding.

I was either lucky or sufficiently flexible to get almost what I wanted (had to buy a one way in First on American to fly LAX back to NYC).

So difficult, but not impossible.