I've never deviated to the Bercy ... I did to the Concorde numerous times. To get from the CDG Terminal to the Concorde you simply walked out in front of the terminal and board the "Air France" bus. The Concorde was the very first stop ... about $10 IIRC. Easy and painless!

The Air France bus seems to be set up to get from the airport to the downtown hotels. It might be easy to get to the Bercy also. Maybe your local Air France reservations office could help?