What I do is use the one-line tool to price an itinerary and see the effect of changing the selling carrier for a flight as well as itinerary changes, trying if possible to make only one change at a time. For example, fly LHR-JNB or LAX-SYD and price it as the operating carrier (BA or QF) and as an AA code share, and as other codes if possible. Sometimes a routing change is needed in order to book a different code, e.g., connecting to/from another flight with that airline's code.

Some examples I've found this way:

• SYD-LAX on QF metal: $175 less on AA than QF
• LAX-MEL on QF metal: $724 less on QF than on AA
• DFW-NRT on AA metal: $20 less on JL than on AA
• HKG-LAX on CX metal: $157 less on AA than CX
• LHR-JNB on BA metal: $318 more on BA (lost my note as to if the comparison was to AA or IB)