I have an ObjectDataSource with a GridView that displays a DataTable.
That works fine, but I'm not sure how to implement the Update.  This
is a more involved update process than most:

1. "Update" should send the changes on the row, update the DataTable/
DataSet, but NOT persist the data.  This allows calculated fields to
be refreshed and re-displayed.
2. A Save button does the actual persistence.

Is that possible using the standard data binding techniques?  How to
go about implementing this?