Another thought, also based on my limited experience. Book the return for sometime far in the future and hope for a schedule change that lets you cancel without penalty. I just did that with the return portion of a AKL-YYZ-AKL ticket from last year. I wanted to re-book using points and when I looked a couple of months ago the refund amount was about 1/3 of what I’d paid for that portion. There was a minor schedule change (15 min?) and I was able to get a full refund. I’ve had that happen with ex-UK tickets as well.