Here is a simple way to hold a small nut in place while getting the screw or Allen cap started. This works well where it’s almost impossible to get at it with pliers or forceps. Use some sticky wax, the type used for holding small items for craft and hobby projects. This stuff works well in holding the nut in the open or box end of a small wrench. This wax is strong enough to allow moving the nut into place (blind) and start the screw from another side. The wax will continue to hold the nut until it is completely tightened, then you just remove the wrench. The residual wax left on the nut is a small amount, which will not interfere with anything.