Twin no, but you could get a pair of knucks and turn them into a weapon focus. knucks are described as being either traditional brass knuckles or plasteel lined gloves.
That said, knucks don't really add to damage really. it would be just as easy to get Killing Fist (which will also allow you to attack spirits and bypass their Normal Weapon Immunity, combine that with Astral Perception and you can attack them before they even materialize), from that you can then get Elemental Strike which acts the same as Elemental Weapon.