Check out the work of Ottawa maker Andrew Plumb. A few months ago, he created the .stl of a four-stud disk, uploaded it to Thingiverse, prototyped it on his Makerbot and then sent it off to fabbing service Shapeways to be output in plastic as well as bronze-infused steel.
In more recent experiment, Plumb used a laser cutter to create plates with holes sized for Lego studs and pins.
At first glance, I’ll have to tweak the designs more for the laser’s kerf. The hole inner diameter is too loose for Lego and too tight for my Shapeways-printed stainless-steel disc buttons, so that places the inner diameter somewhere between 4.9mm and 5.0mm. Will have to break out the calipers when I get home for more precise measurements.