The stopover in HKG on the way back is free. That's not the problem. I just wanted to upgrade the whole way back. But I'm sure not going to waste a Systemwide for the short flight from SIN to HKG. It'll be put to good use on the long haul two days later from HKG to LAX...

Thanks for input. Just wanted to make sure I wasn't missing something. Looks like I wasn't.