I like that idea, but depending on how exact you need to be unless you sharpen the all thread so that the points are exactly centered you will be off some. Any circle pattern can easily be laid out using a compass and some math.
My cure for the centering ( I lay awake at nights thinking of things) is to put the small piece of all thread in a drill and slowly turn it against the table grinder. If I have it still enough I figure it will be as close to center as possible.