If you try and grind the screw (or turn the screw on a lathe, mill, etc) and have a hard time of holding it in your fingers, make a holder for the screw.
Take a round piece of bar stock, drill and tap it thru (M6x1). Then put your screw into the threads. Add another screw to the opposite side of the "tool" and tighten it up with the wrench. Now you have a holder for the screw which you could turn on a lathe or grind it with your fingers to the length you need it.
Hope I make some sense...
