It's not the quickest way, but the safest way I've found is to cut the rubber away from the back of the wellnut. Gripping with thin nose pliers also helps.
Once the rubber has been cut away you find the brass insert is smaller than the hole the well nut fits in and the screw falls away with the insert still on it.
It can be a ball ache, but i've found it to be te safest.............'specially with other peoples fairings
When you refi the screws, really gob them up with copaslip to save having to go thru' this all over again.