is it possible to add data to individual cells?
Definitely, it's possible.
I suggest you the following:
1. Go to http://www.infragistics.com/dotnet/netadvantage/wpfdownloads.aspx page ;
2. Download and install the NetAdvantage for WPF 2008 Vol. 1 product ;
3. Look in NetAdvantage for WPF xamFeatureBrowser ->xamDataGrid->Data Binding and Interaction-> Unbound Fields sample
Unbound Fields sample gives you an idea how to assign values to cells(or add data to individual cells) within a record through code.