Twisted Fate is pretty balanced as far as I'm concerned. He has access to a targetable/semi-spammable stun, as well as an effective aoe nuke in his Q, and stacked deck is even pretty damn good in duels and assassination.
I think giving him MORE tools would be a mistake.
Additionally, his passive is far from useless, it just feels like it because you would be getting gold, anyway. Games are won and lost on how much gold each person makes. TF is able to end a game with 500+ extra gold, which can really help in an item purchase that may have tipped the scales in his teams favor.
IF I was to buff him at all, or make any changes at least, I would VERY MINORLY reduce his mana costs. Even then, it might make it too easy to gank the other lanes.