Different concept. I don't believe you can fly a GPS overlay approach without monitoring the navaid for the approach. Eg you can fly an ndb approach using GPS overlay, provided the navaid is tuned, identified and monitored for the approach. At least that's how I'm led to believe it is done. What QFF wants is to be able to fly the ndb procedure using only GPS in lieu of the ndb when the ndb gets switched off.
Without work done to re assess the approach, this won't happen.