Interesting. I fly to the US frequently to do a trail race (usually PE and use APD / RU to upgrade to J) and I explain to the FA / FSM that I'd need to get up and move around every 2 - 3 hours and stretch and they usually have no issues walking from J - PE - Y & back.
On another situation, I was flying back from HKG, I was in J and friend in PE. I knew they wouldn't let my friend join me for dinner in BP. I was told I could join my friend for dinner in PE but seat next to her was occupied.