For the RTW itin, could you pick something like a 120,000 mile J redemption [Oz-transit Asia-Europe destination-US stopover] and then book another 110,000 mile J redemption [US-Asia destination-Oz Stop] and then just not do either of the return legs?? Call 'em up and say you've had a death in the family or whatever excuse even if you feel like giving an excuse so they could cancel the tickets and maybe re-issue???
To me booking two redemptions in J using a stopver and a destination (however you like to tweak them) would get you pretty close to the 16 segment/5 stopover and save you almost 70,000 miles compared to the actual 300,000 mile RTW J redemption??? US Air may not be too impressed however...