Yep, worked for me too.
Just hand your log book / licence to the cabin crew as you board, together with a polite letter explaining why you want to visit the flightdeck.
I expected a 5 minute visit at best, so when the FA came back and asked if I wanted to go up for the take off, you can imagine the size of my grin. I managed to stay for the entire flight (STN > AMS) & loved every second of it.
I just hope I'm in the position to offer the jumpseat myself in a few years . . .
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Looks like I picked the wrong week to quit pruning.