Edit: I'm also interested on how the fuck you're supposed to play on 3DS
Here's an image on how I do it, although not entirely accurate because I'm holding it in 1 hand. (also wtf this image is huge in the preview)

I pretty much press the D-pad with the "Middle Phalanx" and the joint between that and the "Distal Phalanx"
we had a small discussion of it in the Oldschool Discord server recently and now I'm interested
So the question now is: How do you people hold your controllers when you claw, how does it differ? How do we achieve the most comfortable Claw-Grip?