Flew upper deck Business QF61 CNS-DRW on a 747SP once ...
I'm not sure of the destination, but I think it was DRW. A 767 leaving Singapore had to shut an engine down, and returned. It needed an engine change, so the company sent an SP up to fly the passengers out. The Captain, who was quite a character, made a PA along the lines of "if you look out the left hand window, you'll see two engines...and if you look out the other side, you'll see two more". Amusingly, he found himself flying the 767 not long afterwards.
And on another occasion, I landed in DRW (from CNS in the 767) and on the way to Singapore. There was an SP parked at the gate, which by my reckoning shouldn't have been there at all. So, whilst being refuelled I had a chat to the Captain. They were out of Sydney, bound for Singapore. Turned out that they'd got an engine overheat warning, and had to run the engine at idle (i.e. whatever power makes the warning go away). So, my question was, "what are you doing here though"....where there was zero support for an SP. Just prior to this, the company had made a big song and dance about how Captains were just doing 'stuff' off their own bat, without contacting the company for advice. And we were directed to contact ops control, 'cos they had their finger on the pulse. I completely ignored this memo. So, somewhere near Alice Springs they'd had the issue. The obvious solution was to return to Sydney, but Brisbane and Melbourne were both reasonable options. Anyway, he asked the company. They came back with their preferred option being Singapore, but after a few more comments they worked out that even though the engine wasn't shut down, they only had 3 engine performance, and so could no longer reach Singapore. They stuck their finger more firmly on the pulse, and came back with Darwin. They were asked a number of times if they were sure, and they became more sure on each iteration. So, they took the aircraft to Darwin. Where it couldn't be fixed, there weren't planned flights that could remove the passengers, and as it was middle of the season, there were very few hotel rooms. The eventual fix was to drop a 747-400 into Darwin, with a 5th pod and engineers. Needless to say, everyone went back to just doing 'stuff' after that story got around.