Vref is a good crosscheck for V2 calculation, since they are very close -- Vref30 for F20 T/O, or Vref25 for F10 T/O. For an emergency return, the V2 can be used in a pinch if the PM can't get the FMS set up in time for the landing.
The Vref can be gotten from either the QRH or Preformance Manual, or the FMS Approach Ref page.