procedure TForm1.FormMouseWheel(Sender: TObject; Shift: TShiftState;
  WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
var
  Control: TControl;
  WC: TWinControl;
begin
  Control := FindDragTarget(MousePos, True);
  if Assigned(Control) then
  begin
    if Control is TWinControl then
      WC := Control as TWinControl
    else
      WC := Control.Parent;

    if Assigned(WC) then
    begin
      while Assigned(WC) and (not (WC is TScrollBox)) do
        WC := WC.Parent;
      if Assigned(WC) then
      begin
        (WC as TScrollBox).VertScrollBar.Position := (WC as TScrollBox).VertScrollBar.Position - WheelDelta;
        Handled := True;
      end;
    end;
  end;
end;