Might try looking at longer finish nails of a larger diameter Ross and just make the fixture hole the diameter of the nail and then grind or file down the tip area to .156 to go into your thru hole in the tail end of the plug. I say .156 as that is size I use for thru drilling, oh yeah that equals 5/32 dia.
Turn the plug for the belly hole out of hard wood or plastic in your lathe or buy a couple dowel pins from MSC.
I've been to Joe's and have seen his fixture in action. It is very versatile and does a very good job. Joe made those pins at work or had some guy make them for him I believe. I went my route becasue I have a table saw at home and my band saw is at work so I wanted to be able to do it at home.