From what I know (which isn't much) the Mole just gets a set amount of money based on whatever the production company pays him/her, it has nothing to do with how well they do at the game or at fooling people.
Here is my idea, pay the Mole based on how good they are at costing the group money, yet also fooling them.
Here's the formula:
$1,000,000 - Ending Pot - ($10,000 * Number of people who guess you each week) + ($25,000 * Number of weeks nobody guesses you)
This year it would have been something like:
$1,000,000 - $636,000 - ($10,000 * About 20) + ($25,000 * Maybe 3 times) =
$1,000,000 - $636,000 - $200,000 + $75,000 = $239,000
Gives the Mole incentive to reduce the winner's take, but he/she would have to do it in a sneaky way.
Think Bill would have passed on the dossier using this system, I doubt it.
If the producers or ABC still want a bigger pot at the end, just make the total money higher to start.