You still have the same problem OP. A group of people, at least one of whom if not several will probably tell family & friends, will know this information before others. Which means the people who get in earliest will “know something”. But even if betting opened for everyone at the same time, a certain unknown amount of the pool will be skewing the bets. And that info will quickly leak like the roof on my old Volkswagen convertible, further skewing the betting pool in a manner you wouldn’t see with a true and more random “free market” pool.
I appreciate the ambition. But I don’t believe you’ve completely thought this thru. I wouldn’t bet without a good AI first analyzing the betting trends, to see if it can help me determine if those trends show who the “I already know” crowd is. And of course how they’re betting. Which funny enough is another reason it’s a bad bet: a little bit of math and stochastic analysis can make you part of the “I already know” crowd too! Lolz