There's hidden value in these blue chips that other investors are missing.Bill Ackman of Pershing Square Holdings and Andreas Halvorsen of Viking Global Investors are two highly regarded billionaire-level investment managers. In the second quarter, their companies added new positions in two stocks that just happen to be members of the prestigious Dow Jones Industrial Average, an index that tracks 30 blue chip stocks.Ackman's firm reported a position worth $229 million in Nike (NKE 0.77%), while Viking Globa ...