I am also a *A flyer normally however do know a few things about OW.

I believe that the only way to get from HEL-YYZ is via LHR on BA/AY. You can do YYZ-ANC-HKG-SYD on CX to avoid the US, other wise it would be AA/QF through SFO/LAX. You won't have a problem with sectors within Australia though you may have to go MEL-HBA-SYD to avoid going through SYD twice (on way to JNB). CPT-HEL appears to only be possible through LHR which may be a problem for the backtracking rules.

While this may not be perfect information, someone can correct me and I hope it helps.