The advice you were given makes no sense at all to me. The oneworld award (what I understand of the AA version of same) is miles based, not a 'return' award. If you want to travel A-B-C you add the miles A-B + B-C and that's it. Of course you can also turn it into a return itinerary A-B-A if you want, but you don't have to. So, to turn it into a RTW you could, for example, plan an itinerary LHR-HKG-LAX-LHR, work out the total miles for the 3 segments and then find in the table the award that best fits that total. There's nothing to 'waste', except the miles you 'waste' if you select an award for a maximum of, say, 35000 miles, and your total flown comes to only 34999; in this sense you have 'wasted' 1 mile.