You should be able to upgrade one of these LH sectors with UA miles - remember it is a combersome process involving a paper certificate and so on, but you _can_ upgrade RTW sectors as such. Don't forget a UA SWU will _only_ upgrade on a standby basis and I can tell you from personal experience of more than one flight, it's very nerve wracking waiting.. waiting.. waiting for you to be magically called right before departure for the fabled upgrade seat

Good luck!