Actually, the easiest way would be to add that additional property to your model.
Find attached a sample project - I have added a new field to the Employees table, called IsNew.
I have defined a partial class Employee in the silverlight project and initialized that property to True.
Then, before submitting the changes to the server I set it to False.
Please download the project and observe it.
All the best,
the Telerik team
Let us know about your Windows Phone 7 application built with RadControls and we will help you promote it. Learn more>>