Have you seen these before?
https://www.bearingandengineering.co...TOR+BORDO.html
The idea is that you drill into the shaft of the screw and the easy out grips inside and spins the shaft out. If not, then I have been doing it wrong. It will probably be surgical to try and drill into the shaft of a rail mounting screw, but if you get the right sized EZY out, although you may need to grind the tip of it off, it might be able to grip inside the rounded hex head.
The other option could be to solder an allen key inside the rounded hex head, in doing so, it would also heat the locktited shaft of the screw.
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