Well after a little test driving, this configuration may be worth refining. I used an old miter gauge 'tongue', an oak runner and an old piece of melamine.
The two screwheads act as a stop. There is enough overhang at the front of the saw that I just hold the jig in place by leaning against it.
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Drill a hole in the blank to fit the "adjustable positioner" screwhead
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The runner allows me to slide into the initial cut. The screwhead 'stops' . . . well, stop me.
Give the blank a spin and there you are.