Originally Posted by Steve in Olympia

There are so many false statements in this post, it is hard to know where to begin. Here is a brief start:
1. Yes, you CAN add the return flight to an existing booking. I (and others) have done it dozens of times, via phone.
2. Yes, you CAN merge bookings, as demonstrated by previous posts on this thread. I have done it, and several others have, as well.
3. Making a booking it and then cancelling it --- a strategy that is foolish, risky, and unnecessary.

The simple answer: Book the outbound voucher flight on-line, when the seats initially become available. When the inbound seats become available, call a service center to add the inbound flight to the outbound voucher booking. This may involve calling Japan. See this thread for more detailed discussion. Most importantly, ignore everything in the post quoted above. (Poster should seriously consider deleting it.)