[bartsau]

With the scrivets I have found you can sometimes depending on their condition get them out using a screwdriver lightly with the back edge of a blade under the edge pushing it out.

Failing this I use a drill bit about the size of the shaft of the actual screw section maybe a touch larger drill with it on forward to lock the drill in the screw and then reverse it. I have it down to a fine art in that on reverse the screw comes out attached to the back of the drill bit.

Hope this helps. Oh and they are bloody expensive little buggers to purchase!!