Yea, I just got into a rhythm of always booking via co.com. It was not difficult to check for upgrades on Alliance partners, and look at the Terms & Conditions, which has the dreaded "Codeshare flights not eligible" message.
And so it goes ...
So, is it confirmed that I have no recourse? (can't believe that I'm still looking for a loophole ...).
No recourse. You can only use CO miles on a UA flight if booked in Y or B classes. This will change later obviously as the programs are integrated. But not right now.