Add a property to the RadGridView that provides a distinct template for adding a new row.
Sometimes you have classes with no default constructor. Those classes may have properties that are read-only after construction. This cannot be handled in the RadGridView, because you only have the choice of a CellEditTemplate. (I'm envisioning something akin to the RowDetailsTemplate.)
Example: I have a class that defines a invoice match for payment application. Once the invoice is set it cannot be changed. The user can still edit the match, but they're only allowed to edit the amount to be applied.