It's only been done by hypermilers intent on breaking the record. Basically, a constant 25 mph, straight flat road, no AC/heat, and all electronics possible shutdown. I imagine they may also have used different tires and maybe put a lot more air in them than normal. It's nothing you can achieve in "normal" driving. However, it is possible to go close to 400 miles in an LR RWD if you keep your speed at 55 mph or less on the freeway and refrain from AC/heat. In Oregon, this is possible if you stay in the truck lane aka no one will run over you . From what I've read of other states it might be suicidal. I used to drive 54 mph on I-5 all the time when I was returning from a long "mission" in the Leaf. As long as I stayed in the truck lane everything was cool.
That was meant to be just an IT geek joke. However, I never ever experienced consumption that would have given me more than some 260 miles of range for a full charge.