I would think that if you require an extender on ANY airplane, there is perhaps an issue with your size. They are typically looking for agile, fit people for the exit rows. Even if you work out and are in good shape, they have to make a rule about it because most people that require an extender are over 300 lbs and are definitely not fit and agile. Obesity limits mobility and flexibility and causes all kinds of knee and back problems. Granted it sounds like you know what you are doing and could open the door in an emergency, but they aren't going to make special allowance for "extra aircraft knowledge" in obese passengers.

One one flight recently (on a small UA commuter, I think it was Mesa), a woman (not obese, just normal size) boarded with her foot in a boot of some type, the kind you get if you hurt your ankle. She was using one crutch, and the flight attendent helped her with her backpack and helped her to her seat - which was in an exit row. I couldn't believe the FA was OK with leaving her in that row!!!