Estimated range is not fool-proof. Common sense should be applied to everything - even technology packed car.
Can you toggle the regenerative effect when you lift off the pedal? Like just when your about to crest a hill, they quickly toggle it on once you get + over the speed limit on the downhill side?
I can hit some pretty astounding numbers in my TDI Beetle vert with really simple tricks but that does rely on the fact that I can pretty much stay in high gear so engine braking isn't a factor, only danger being stalling. Engine uses no fuel without throttle input unless you put the clutch in.
In either scenario, I believe both the motor and disc brakes are utilized when the brake pedal is depressed; however, the general theme is that more kinetic energy is lost to thermal from disc brake friction in the Low scenario.
My thoughts are that regeneration of the battery is encouraged, but the marketing of the Model S appears such that Tesla Motors wants to deliver EV luxury & performance first, and foremost and then cleverly extend it behind the scenes in such a way that the user need not think about it. To me, it's not all that different from flagship smartphones. Actively 'hypermiling' a flagship smartphone for battery life would compromise many of the flagship features... which aren't suprisingly luxury and performance.
You can, but this would slow you down more than gravity, the transmission, and the friction of the road alone would.
The only thing you can really do is change to neutral. Dual-clutch transmissions in high-end sports cars have already been doing this for years, though they don't do it based on the angle of the road surface, since if you're going fast enough, it's beneficial to do it as often as possible.