I just booked a round trip flight from IAD to PEK with a stopover in HNL using ANA miles. The trip consists of legs on Asiana and United metal with no actual ANA metal. I was successfully able to book the whole trip on business class except for the last United leg from HNL to IAD which is in economy. The ANA agent told me that I could call back at any time if I find that an award seat opens up in business on that flight and they could change it.

Is there any way to "waitlist" this leg either through ANA or United? Can I call a United agent and explain how I already "paid" for business using ANA miles and have them code the reservation accordingly? What are my other options? What am I missing?

If I can't waitlist, what is the best way to keep an eye out for an open saver award seat on that flight considering expertflyer doesn't do United? If it comes down to the day before the flight, when do they open up the unused seats for award reservations? 24 hours? Should I call ANA or United at that time?

Thanks!