Times have changed with respect to oil changes. The motors are much tighter and much cleaner. There simply isn't as much of a need as there used to be back in the day when there was tons of blow by and tons of fuel vapor entering the crankcase. These are really the only reason oil needs to be changed to begin with. It doesn't really get "dirty". It gets diluted by fuel and the additive package wears over time. It just discolors from heating. In addition to cleaner motors, the synthetic oils themselves get better every day.
The algorithms and sensors used to extropolate the remaining life of the oil are pretty damn impressive. If the car says it doesn't need an oil change, it doesn't need an oil change. I don't fault BMWNA one bit for sticking by their policy. I think THEY know better than anyone what is and isn't good for their cars. If you want something done out of sequence, I don't see why you wouldn't feel you need to pay for it yourself.
Rules of thumb like changing every xxK miles or xx months are arbitrary. Depending on your driving habits and how tight your motor is, the requirements can and will vary widely. The worst thing that ever happened to automotive maintenance was Jiffy Lube's claim that oil needed to be changed every 3,000 miles. What a crock of BS. Pure marketing hyperbole.
From it's introduction, Mobil 1 has professed it could run out to about 10K miles before a change. I believe their newer long life lines indicate they can go 15k or better. If anything, this would be counterproductive on their part since they'd sell lots more oil if everyone changed every 5k miles.
The bottom line is that if you want to operate outside the rules it should be your dime. And while I don't necessarily agree with the fact that the SA shrugged it off because you're leasing, what he said is absolutely correct. You're renting the car. If you were driving a Ford Taurus you rented from Hertz, would you be compelled to have its oil changed followed by a nice detail? If you think you might want to buy it out, then do whatever you would as if you had bought it. But I think it's unreasonable to ask them to bend the rules to appease you.