Unfortunately that is unlikely to happen now that the BA/QANTAS tie up has finished. But BA are partnering with CX between HK and MEL so this could apply in this instance. But as a consumer it is always worth checking if there are codeshares with the other operating carrier as you do get quite large disparities in price from time to time – and it will all depend on how the codeshare agreement is worked out revenue wise (e.g. – do the codeshare airline get an allocation of seats that is up to them to then sell at whatever fare they determine?)
Anyway we have gone way off the original theme of the post – is this allowed?!