Hi GingerDives, sorry for the delayed response... I don't frequent this board that often.
I found this video of a device that stabilizes a boat.
But while everyone else is trying to rock the boat for the demonstration, look at the bald guy in the plaid shirt on the left who is NOT rocking the boat. Notice how as the boat rocks, he is keeping his body in the same location (although he is going up and down). He does not "rock" with the boat. Instead, he's letting his legs/feet "surf" the boat so that even though the boat is tilting, he is not (relative to the Earth). He's effectively always vertical.
I was doing this on my last boat dive and was noticing how no one else was doing it (even the boat captain and dive master). But I'm guessing they are motion sickness resistant... unlike me. I used the same technique on a cruise ship in rough seas and it worked too.
Here's another one. This guy looks like he keeps tilting, but if we could see a land reference, I'm betting he looks "vertical" the entire time.