How can I programmatically display the window system menu (title bar)

There is no non-client area in my dialog because I want to draw a custom title. But this means that the system menu is not displayed when the user clicks on the title.

I changed WM_NCHITTEST to reply HTCLIENT to my header and I can record the WM_NCRBUTTONUP message, but I need help demonstrating the system menu, I cannot figure out how to do this properly.

So far I have this:

void CSkinnedDialog::OnNcRButtonUp( UINT nHitTest, CPoint point )
{
    CMenu* pMenu = GetSystemMenu(FALSE);
    if (int cmd = pMenu->TrackPopupMenu(TPM_RETURNCMD, point.x, point.y, this))
        SendMessage(WM_SYSCOMMAND, cmd, MAKELPARAM(point.x, point.y));
}

void CSkinnedDialog::OnSysCommand(UINT nID, LPARAM lParam)
{
    if ((nID & 0xFFF0) == IDM_ABOUTBOX)
    {
        CAboutDlg dlgAbout;
        dlgAbout.DoModal();
    }
    else
    {
        CDialog::OnSysCommand(nID, lParam);
    }
}

LRESULT CSkinnedDialog::OnNcHitTest( CPoint point )
{
    LRESULT res = CDialog::OnNcHitTest(point);
    ScreenToClient(&point);
    if (res == HTCLIENT && point.y < m_nFrameHeight)
    {
        res = HTCAPTION;
    }
    return res;
}

void CSkinnedDialog::SysMenuAddAboutEntry()
{
    // Add "About..." menu item to system menu.
    // IDM_ABOUTBOX must be in the system command range.
    ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
    ASSERT(IDM_ABOUTBOX < 0xF000);

    CMenu* pSysMenu = GetSystemMenu(FALSE);
    if (pSysMenu != NULL)
    {
    pSysMenu->AppendMenu(MF_SEPARATOR);
    pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, "About...");
    }
}

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