What is pen spinning you ask?
Blueprint (big image)
Goal
I don't think it'd be possible..
4 limbs could constitute 4 fingers (fully articulated), so we'd be missing a thumb (unless someone (would most prob be MacSparrow honestly) figures something out with the butt hidden parts.)
But then again they could only move on one axis, doubt you could effectively mix and match two axis' at the same time, and it'd be extremely hard to replicate the movements of the hand you can see in the gif you posted. You'd lose a lot of the momentum required for most of the tricks if you cant move your hand as fast as that...
I can do a couple of tricks myself, and no matter how hard I think of the way to make it, it's never fully practical :l
I like the Idea, but I really doubt anyone can make it good enough to be enjoyable.
I actually agree on the fact that a mod like this would be so fucking awesome.
Even still, i really don't think there's a way to do it properly for MULTIPLAYER.
Maybe in singleplayer if we use the both toris to create the hand ?
A tori is basically :
17 No joint.
20 Joint.
Wich meaaaan
17 x 2 = 34
20 x 2 = 40
34 + 40 = 74
So, more likealy 74 parts.
And 40 are joint.
Seriously, i think we can do something in singleplayer.