Just wanted to add my DP.

Had 2 international awards with the longhauls in Business and the short flights in economy due to availability at booking. Found First availability only due to searching connecting itineraries (in my case, I had AUS-DFW-NRT booked and AUS-DFW came up empty but a new search for AUS-DFW-NRT with a different DFW-NRT flight showed First availability on AUS-DFW). Called in multiple times and spoke to different reps and supervisors who said they could not upgrade the segment as the entire itinerary would need to be available. Twitter support was no help. Finally got hold of a supervisor who saw the availability on other itineraries and did some sort of manual "overbooking" as she called it and pushed me into First on both flights. So it still can be done.

HUCA and be persistent.