FrogAddict,
I start by drilling a 1" hole in a piece of hardwood with a hole saw. Take the first piece of wood and place it on another scrap of hardwood remove the hole saw's 1/4"pilot bit and run the hole saw through using the first hole as a pilot guide.You can use the pilot bit to just barely enter the second piece or find the center of the new plug by other means later. Or you can cut 3/4" off of a 1" dowel.
Now drill a 1/8th inch hole into your plug with a drill press. Drive a machine screw through the center, add a washer and nut to hold it steady and chuck it into your drill press. Once it's in your drill press use a square sanding block to true up the circle and grind in the radius. I used a lathe chisel while it was in the drill press. A lathe would be nice for this step and probably a lot safer than how I did it. (might not want to do this part in an OSHA inspected shop) I also had to file down the threads of the screw a bit to get it into my dremel chuck but it works.
After a test spin I glued some sand paper off of an old belt sander belt. Be sure to cut to the exact length. Use a bunch of rubber bands to hold it tight while the glue dries. Sanding belts are tougher and last longer but they are rigid so make sure that you bend and "knead" it so that it will conform to the radius of your plug.
After the glue dries, remove the rubber bands, chuck it into the dremel and sand away. I have to slow down the dremel a bit because its heavier than the factory sander and it still causes more vibration. I only use it for rough shaping.
I need to make another with a tighter radius
Here is the one I use.