Here is the exact wording of the battle of wits (Vizzini's answers removed):
In that case, I challenge you to a battle of wits. Good. Then pour the wine. Inhale this, but do not touch. What you do not smell is called Iocane powder. It is odorless, tasteless, dissolves instantly in liquid, and is among the more deadly poisons known to man... All right. Where is the poison? The battle of wits has begun. It ends when you decide and we both drink, and find out who is right... and who is dead.
I submit that under the phrasing of the challenge, Vizzini could indeed have won... had he drank out of the bottle.
He would have logically answered the question: you would not have entered a battle of wits where there was a chance of your death based on a 50/50 guess. As such, there has to be a catch, something that guarantees my death and ensures your survival. The simplest answer is that you have the antidote (or an immunity), and poisoned both glasses.
But you specifically asked me to pour the wine and never touched the bottle. If we watch the video in question, it indeed looks as though there's still wine left in the bottle based on how Vizzini pours.
Under the rules set out by the Dread Pirate Roberts, Vizzini only had to "drink," not drink from one of the glasses. By choosing the bottle, he would have saved his own life and chosen a legitimately clever solution, winning the battle of wits. At the very least, with both men alive it would have been a tie.