Just make your own guid rail out of a straight button and a thin piece of sheet material. Like in the picture below. Although who ever made that used a much thicker base than I do.
I would use 4mm ply, or ideally what we in the UK call hardboard (Shiny one side, rough the other) so the underside grips a bit and on top the saw slides nicely.
As long as you make it over-sized then your first cut will create your cut/guide line and the base material will also then be a splinter guard of sorts. Small section of sheet material on the far side of the baton is ideal for clamping.
This is what I used to use all the time before I discovered actual track saws.
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