MouseBinding defined in code

I am trying to insert a textblock into the column header of a datagrid when autogeneratecolumns="true".  I have the following but when I have set a beakpoint in OnColumnHeaderClick the object is null.  I was hoping to get either the textblock object that was clicked or a MouseEventArgs.

public ICommand ColumnHeaderClickCommand { get; private set; }
private void dataGrid1_AutoGeneratingColumn(object sender, DataGridAutoGeneratingColumnEventArgs e)
{
    var textblock = new TextBlock();
    textblock.Text = e.Column.Header.ToString();
    textblock.HorizontalAlignment = HorizontalAlignment.Stretch;
    textblock.VerticalAlignment = VerticalAlignment.Stretch;
    textblock.InputBindings.Add(new MouseBinding(ColumnHeaderClickCommand, new MouseGesture() { MouseAction = MouseAction.LeftClick }));
    e.Column.Header = textblock;
}
private void OnColumnHeaderClick(object obj)
{
}