You mean, a throwaway segment somewhere else? That might work on the return but it won’t work on the outbound unless OP actually intends to fly it. (It’s also against the rules, but I know you know that).

I saw codeshare inventory down to P without an extra segment on some dates, but the price remained high. The discount fares must exclude UA-operated-by-OZ. The only way adding another segment would help would be if there is a fare table where they forgot to exclude these flights from the discount fares.