I've never been SE, but got to sit in the jump seat YYZ-LHR back in the 80s in a 747 if memory serves me correctly. I was waiting to board last since I didn't see any reason to get on early. There was an older lady who I guess was on Standby and she was told she'd have to sit in the jump seat. I had no idea what it meant at the time, but being the young gentleman that I was I said I'd be happy to sit there instead. They moved me back to J for the meal, but other than that I sat in the cockpit for most of the flight. It was awesome!