Well Dave with a little math and a very expensive vise, oh yeah a Bridgeport helps
you can find the center of the plugs and drill away. Adjusting the handles for varying dia. I realize this is not something many people have laying around. I have been thinking of a way to use a drill press and vise to do a similar way. If all the plugs were of the same dia. then you could just set the vise and you would be on center but that would be too easy. I think maybe a fixture which would orientate the plug using the thru hole. Maybe a pin inserted into each end, adjustable for different length. The fixture would be mounted on drill press so the pin center line would be on center of the drill press spindle, then plug dia. would not matter. I will do some thinking on it. You could always just do it by eye with a hand drill
. Paul