Casting a base class to a subclass

Using the ADO.Net DataSet designer, I create a DataSet named dsUISupport, with a DataTable named dtCustomer.  So, the designer autogenerates a strongly typed class something like this:

dtCustomerDataTable : DataTable

Now I want to add some functionality, so I add my own subclass:

cCustomer : dtCustomerDataTable

Now, what I am doing is, in a Windows Form, I have a DataGrid that uses dtCustomerDataTable as a DataSource (indirectly, via BindingSource).

Now, when the user makes a change to the DataGrid, the DataSource generates a RowChanged event, in the event handler, I use a dtCustomerDataTable.GetChanges() to get a dtCustomerDataTable object with the changes that were made.  Now, I want to cast this object to a cCustomer object, which is my own subclass.  I understand I can't do this directly, because it isn't really a cCustomer object.  So, perhaps casting is not the word.  But I think that should in some way be able to get a CCustomer object with the same dtCustomerDataTable base class, if I am prepared to do some fixups.  Could I new a cCustomer object and then somehow assign the dtCustomer DataTable to the base class?  Or should I do some kind of DataTable.Copy to copy over the members of the base class?  Please advise.