BLOOMBERG BETS?

There's a story on the radio about how NY mayor Mike Bloomberg has promoted healthy habits, such as nutritious school lunches and anti-smoking measures. One thing in it caught my eye:

Bloomberg's weaknesses are red wine, hot dogs and the occasional hamburger. If he overindulges, there's a price to pay: He has a weight-loss wager with longtime friend Peter Grauer, the CEO of Bloomberg LP. They weigh in every six weeks, and whoever is over his goal weight _ Bloomberg's is 169 _ must fork over cash to charity.

Now Mayor Bloomberg is listed in the Forbes 400 as having a net worth of $5.1 billion. How much of a wager does he have to make so that he would really care if he lost? A million? Ten million? More?