Notknow said:
Have someone really tried to do scientifically design a comfortable box or "hole in the box" for those "stuck in a wall" / public use situation on hentai or it's just not possible?

Dunno, but I'd assume the question of comfort lies more on the position of the body than the hole itself, since we can't really stay still in a weird position without moving for a long time.

If not for that, it's just a matter of measuring someone's butt, cutting a hole, covering the edges with foam, and laying down a mattress like this. Maybe holes for the legs too.