I've made plugs with a hole saw that turned out pretty OK. I drilled out the knot with a hole saw and made the plug by removing the center drill after getting

I've made plugs with a hole saw that turned out pretty OK. I drilled out the knot with a hole saw and made the plug by removing the center drill after getting about 20% through the plug board. I used a slightly larger saw for creating the plug and then sanded the difference (after marking the plug with a set of calipers) on a belt sanding jig, which allowed me to essentially turn the plug. The end result wasn't as good as Paul's, but it allowed me to get the job done.