Mouse click in non-item area of CListBox

I want to know when the user has clicked in a CListBox, but outside of any item. I was hoping to get some notification in the containing dialog so I can process the point to determine if it is inside an item via mylistbox.ItemFromPoint(flags,outside). But clicks within the listbox don't seem to result in such events. What event should I be looking for in the parent dialog, and what needs to be set up to enable it? I really don't care if it is a click or just mousedown.

My purpose for this is to deselect all items if the user clicks outside of any item, with mylistbox.SetCurSel(-1).

Addendum: This is the full code for the class implemented as suggested by @mercurydime.

(Header)

#ifndef INCLUDE_CMYLISTBOX_H
#define INCLUDE_CMYLISTBOX_H

class CMyListBox : public CListBox
{
public:

    CMyListBox();

    void                allow_deselect( bool allow = true );

protected:

    bool                m_allow_deselect;

    afx_msg void        OnLButtonDown( UINT flags, CPoint point );

    DECLARE_MESSAGE_MAP()
};

#endif  //  INCLUDE_CMYLISTBOX_H

(Body)

#include "stdafx.h"
#include "CMyListBox.h"

CMyListBox::CMyListBox()
    : CListBox(), m_allow_deselect( false )
{
}

void CMyListBox::allow_deselect( bool allow )
{
    m_allow_deselect = allow;
}

BEGIN_MESSAGE_MAP( CMyListBox, CListBox )
    ON_WM_LBUTTONDOWN()
END_MESSAGE_MAP()

void CMyListBox::OnLButtonDown( UINT flags, CPoint point )
{
    if( m_allow_deselect )
    {
        BOOL outside( TRUE );
        ItemFromPoint( point, outside );

        if( outside )
            SetCurSel( -1 );
    }

    CListBox::OnLButtonDown( flags, point );
}

1. Use the Class Wizard to create a class derived from CListBox:

• Ctrl+Shift+X

• Click the down arrow on the Add Class button

• Select the MFC Class menu item

• Make sure the base class is set to CListBox

2. Add a message handler for WM_LBUTTONDOWN

• Ctrl+Shift+X

• Click the Messages tab

• Double-click WM_LBUTTONDOWN

3. Add your ItemFromPoint code inside the handler

void CMyListBox::OnLButtonDown(UINT nFlags, CPoint point)
{
    BOOL bOutside = TRUE;
    UINT uItem = ItemFromPoint(point, bOutside);

    if (bOutside)
    {
        // do whatever
    }

    CListBox::OnLButtonDown(nFlags, point);
}