Unfortunately, while UA can open revenue business space to displaced award holders on its own metal, it can't do the same for partner metal. If you're lucky you might get an agent who's willing to call NH and ask them to open I space on NGO-CTS, but NH has every right to say no in these cases.
You can also look for NH I space on NRT/HND-CTS on the days you want to travel. Worst case, I think the morning GUM-NRT on the 772 with half a day in Tokyo might be enjoyable, or else the later GUM-NRT on a 73x, connecting onto the (very short) evening NRT-CTS. Both those give you a decent run in F/J with only a short hop in Y.