Code:
// from wincore.cpp

BOOL CWnd::SubclassDlgItem(UINT nID, CWnd* pParent)
{
    HWND hWndControl = ::GetDlgItem(pParent->m_hWnd, nID);
    if (hWndControl != NULL)
        return SubclassWindow(hWndControl);

   ...
}
After generating unique item ID, you can use SubclassDlgItem, which effectively calls SubclassWindow. You can call SubclassWindow without item ID, as I suggested in my first post.