This is a great idea! Especially for hit and run, but it does lack escape. Here's an idea: does Twitch's passive true damage poison proc spell vamp? If so something like Hextech Gunblade or Will of the Ancients could really give him some nice bonuses, since his E works on AP as well. And Liandry's Torment might be an idea, since the poison might/will proc the effect repeatedly and let it last three times as long.