It's not possible, although there are claims you can do it through a glitch in-game.
From Zelda Informer:
Well, this video claims to be a glitch that allows you to enter the
bathroom and get closer to the completely-naked Gaepora. From what I
can tell it is most likely a hack as we cannot replicate the glitch,
and the video shows that the game has already been hacked to remove
the shield meter, rupee amount, and to add a superman jump. So, its
not necessarily a glitch per se.
With that said, the video below shows Gaepora bathing up close, who
happens to have no legs, or other parts for that matter.
Understandably, there's no reason to animate below the water seen as
we're not supposed to be hacking and glitching our way into the tub