As the sibling/nephew posts indicate, the bet is a good deal for anyone who has faith in The Predictor's ability to predict actions.
We also have a huge range for our bet to cover varying levels of certainty.
Again, this is not win-optimizing, but risk-averting. I am pretty sure I am being generous with the technical definition of risk aversion, but that is not material to my suggestion.
The paradox exists because there is no clear best strategy. The best you can guarantee (without resolving the paradox) is $1000, if you always take A and B you will net at least $1K, with the potential (depending on paradox resolution)for $1.001M. My suggestion aims to increase the guaranteed minimum essentially by purchasing it with the decreased maximum. $500K is really just a Schelling point, but unnecessary.
A bet of $999K is the breakeven point - any bet less than this amount increases your guaranteed minimum such that this guaranteed minimum is always greater than the $1000 which is the guaranteed minimum of taking A and B. Since The Predictor is (depending on version of the paradox) either infallible or nearly so, it seems reasonable to me that you can find someone to take a bet at <$999K.