Thanks for confirming, Artpen. I knew the OLCI offers existed with cash only, so that's why I hoped they could be available over phone or website. But that seemed riskier to wait for OLCI (not even sure if always an option for international check-in) than to just try miles + copay option.
It seemed strange that no upgrades with instruments were processed at 24 hours before the flight, but it worked out in our favor this case.