<Button x:Name="btnProcess"
        Content="Process"
        Margin="10"/>

public void Run()
{
    Shell shell = new Shell(new Customer());
    shell.Show();
}

public Shell(IPerson person)
{
    InitializeComponent();
    btnProcess.Click +=new RoutedEventHandler(person.Process);
}

public class Customer : IPerson
{
    public void Process(object sender, RoutedEventArgs e)
    {
        Button theButton = (Button)sender;
        theButton.Content = "Customer processed.";
    }
}