Winforms DataGridView Column with a custom header (Combobox + NumericUpDown control in this instance)

ComboNumericHeaderCell.cs

public class ComboNumericHeaderCell : DataGridViewColumnHeaderCell
{
    public readonly ComboBox _comboBox;
    public readonly NumericUpDown _numericUpDown;

    public ComboNumericHeaderCell()
    {
        _comboBox = new ComboBox();
        _numericUpDown = new NumericUpDown();
        _comboBox.Font = Control.DefaultFont;

        _numericUpDown.Increment = 1;
        _numericUpDown.Value = 10;
        _numericUpDown.Size = new Size(40, 20);
        _numericUpDown.Font = Control.DefaultFont;

        _comboBox.MouseClick += new MouseEventHandler(MouseClick);
        _numericUpDown.MouseClick += new MouseEventHandler(MouseClick);
        // TODO - Wireup necessary events
    }

    private void MouseClick(object sender, MouseEventArgs e)
    {
        Debug.WriteLine("x:{0}, y:{1}, button:{2}", e.X, e.Y, e.Button);
        OnClick(new DataGridViewCellEventArgs(ColumnIndex, RowIndex));
    }

    public string ComboBoxValue
    {
        get { return _comboBox.SelectedValue.ToString(); }
        set { _comboBox.SelectedText = value; }
    }

    public decimal NumbericUpDownValue
    {
        get { return _numericUpDown.Value; }
        set { _numericUpDown.Value = value; }
    }

    protected override void Paint(Graphics graphics, Rectangle clipBounds, Rectangle cellBounds, int rowIndex, DataGridViewElementStates dataGridViewElementState, object value, object formattedValue, string errorText, DataGridViewCellStyle cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle, DataGridViewPaintParts paintParts)
    {
        base.Paint(graphics, clipBounds, cellBounds, rowIndex, dataGridViewElementState, value, formattedValue, errorText, cellStyle, advancedBorderStyle, paintParts);

        _comboBox.Location = new Point(cellBounds.Left, cellBounds.Top+3);
        _comboBox.Height = cellBounds.Height;
        _comboBox.Width = cellBounds.Width - 41;

        _numericUpDown.Location = new Point(_comboBox.Right + 1, cellBounds.Top+3);
        _comboBox.Height = cellBounds.Height;
        //_comboBox.Width = FixedWidth;
    }

}

SpecialColumnHeader.cs

public class SpecialColumnHeader : DataGridViewTextBoxColumn
{
    ComboNumericHeaderCell headerCell = new ComboNumericHeaderCell();

    public SpecialColumnHeader()
    {
        //this.CellTemplate = new DataGridViewTextBoxCell();
        this.HeaderCell = headerCell;
        this.Width = 150;
    }

    protected override void OnDataGridViewChanged()
    {
        if (DataGridView != null)
        {
            this.DataGridView.Controls.Add(headerCell._comboBox);
            this.DataGridView.Controls.Add(headerCell._numericUpDown);
        }
    }

        
}