Try using a flat-bladed screwdriver to push the spring down (you may want to put some tape on the screwdriver to keep from scratching the gun), and glue the screw to another scredriver with some super glue. Put the tip of the screw next to he tip of the screwdriver and slide the screwdriver off the hole, following it with the tip of the screw. When the screw is in the hole, tighten it down, pop the screwdriver loose from the screw and clean off any superglue residue with some acetone.
I’ve been using a flat-bladed screwdriver on the spring/rod, but the biggest problem is working the screw/washer at the same time. Two hands and all that...
I’d thought of a magnetic screwdriver, but don’t have one anywhere near small enough. I’ll try the super glue angle. Thanks!