I tried to use a GPU to upgrade IAD-HNL on a less-than-W class ticket. My experience with the online system was that although it looks like you can use a GPU to upgrade IAD-HNL it doesn't actually upgrade you. In the end I had to PM UA Insider, who helped me (thanks again Shannon!

). Next year I plan on saving my RPUs for the EWR/IAD/IAH-HNL non-stops.