Locking Chart Data area

Maybe create Pivot Chart directly from Data Model not from existing Pivot Table (Workbook Data Model)
but I don't know if it will be possible with Ex2007

You can try with Power Pivot adapted to Ex2007

or

create first PT then create PChart (you can hide this PT if you want)
next
create second PT with the same parameters like first PT and with the second PT you can do what you want and PChart doesn't change.

also you can try PT Options - Data - Retains item deleted from the data source - Max