In PMUA, standbys were not allowed for international flights. Even if they are allowed now, the ANA segment would cause a problem. The agent wouldn't have access to the ticket in ANA's system, and coordination with ANA would be required. It's unlikely that an agent would rebook you on the nonstop unless there is something that prevents the original itinerary from being flown, such as a canceled flight or a delay that would cause a missed connection.

You could rebook the ticket, although that would incur a change fee and possibly the difference in fare (which could be rather high at the last minute).

You could ask a ticketing agent when you get to the airport. Sometimes the Japanese agents are surprisingly accommodating.