I'm trying to use betting to force people to put their money where their mouth is, with the expectation that they won't (but if they do, then I make easy money).

As you said, the consensus position is probably already factored into the price of the investment, and many factors besides increased proof of the consensus position will presumably influence future price movements.

It might be worth pointing out that if denialists agree that the consensus position is factored into the price of relevant investments, then they're in position to make money by arbitrage.

Still doesn't get me to a position where I can make them bet against me or back down, however.