With that in mind, you could try starting to book as an award, and if the flights you want are available, select them. At some point, it will tell you they are available for purchase for $X, and there is a button to click to buy. You'll also get the flights booked as operating carrier flight numbers instead of as UA codeshares, I would suspect.

My disclaimer is I've never tried to ticket a revenue flight this way, so potentially possible it could err out, but the option has definitely been available everytime I have looked up an award.