Re: Would it be possible...
No, The diameter of the hex poles is larger than that of the slugs. You could possibly drill out the bottom half of the hole for the slug to fit in to but, you will have a gap at the top of the coil between the slug and the coil. Also, to do this kind of mod, you better be really handy at using a drill press and also have the right tooling to line up the exact center of the hole with the drill bit! Not a project for the novice!
They could be easily replaced with the standard flathead poles though! Just unscrew the hex and screw in the new slot screws. I belive the are 5-40 filister head screws!