Sir poorcol1964 . . . .
Obviously . . .if the OTHER end of the screw has an accessible Phillis or standard cross slot head, just do your tightening at that end.
Or if . . . .
You just have a few units to deal with, and the situation is dealing with standard machinists profile . . .wherein the
internally installed screw is expected to be extending 2-3 threads out of the nut . . . . . but no more..
Amongst all of my long nosed pliers collection, I have a few that will let each end nib extend down into those slots.
I just hold the open ended handle of the pliers cross handed have them just drop down in the slots and use my second hand to span the very ends of the pliers to compress and hold the nibs down within the slots.
Then both hands rotate the pliers in tightening, until a new grip is required.
Third option is to pick an alum-i-ninny-yum-yum spacer that is already tapped or has a hole within it that just a bit larger than the external thread size of the screw. Then you either use a Dremel with cut off wheel / or / flat mill file to reduce the end of the spacer to that to a reverse of the required mating profile. The other end of the spacer then
is transitioned to a "T" or 'L" profile with an inserted long screw.
Or you chuck it in your adjustable tap wrench . . . or a la Neanderthal style . . . just grab the end with a pair of Vise Grip pliers.
Only now, just now having seen his closely timed Minders answer . . . . I have also done that with a standard screwdriver and a Dremel tool with a cut off wheel to cut the central slot IF there is no long extended screw involved, or it can be cut back..
73's de Edd