I tried using nexus cape with someone at the top of the mountain with a mimeo stone. The stone grows dark and shatters when you finish using the item. You can't use that to get up there to get the feather, unfortunately.
That has a few people claiming to get it legitimately. Otherwise, yes it sounds like hacker-bait, and I recall reading a thread on KI or BG about someone getting auto-jailed as soon as they got it in their inventory.
If the stones around the base of the mountain disappear at some point of the moon phase or certain month of the game year, it's possible with flee + boots...