HWND hParent;
WNDPROC wpEdit;

LRESULT CALLBACK EditProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {

   LRESULT lRes;

   if(msg != WM_MOUSEMOVE) {
      lRes = CallWindowProc(wpEdit, hwnd, msg, wParam, lParam);
   } else {
      return DefWindowProc(hwnd, msg, wParam, lParam);
   }

   if(msg == WM_LBUTTONDOWN) {
      // code
      MessageBox(hwnd, TEXT("lbutton click test"), TEXT(""), MB_OK); 
   }
   return lRes;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {

   // bits of code
   static HWND hEdit1; // handle to edit control

   switch(msg) {

      WM_CREATE : // bits of code
                  hParent = hwnd;
                  wpEdit = (WNDPROC) SetWindowLong(hEdit1, GWL_WNDPROC, (LONG) EditProc);  
                  // bits of code
                  break;

      WM_DESTORY : // bits of code
                   SetWindowLong(hEdit1, GWL_WNDPROC, (LONG) wpEdit);
                   // bits of code
   }
   // bits of code
}