Looking at the map of the kangaroo, I imagine that there would have been some very sharp turns and banks to get the angles depicted. Any comments @jb747 on how interesting/exciting that would have been for the crew and what it would have felt like if passengers were on board?I've also heard from one of the pilots who was on OEJ's flight to the USA. I was curious about exactly how they'd flown the kangaroo.
The FMC has two routes. Primary and secondary. Generally, if you need to make large changes to the route, you'll copy the currently active route to the secondary. Make the change whilst it's in the secondary section, and when happy with it, swap it with the primary route. In this case the flight to the USA was kept separate to the kangaroo, and the position swapped when it was time to fly it. Longer legs were flown in NAV, with the FMC controlling the aircraft to fly the exact track. Most of the turns were done in heading/track mode, with the bank controller being used to get the maximum available bank angle.