Have you tried simply using a good quality steel rule with a ruler stop on it ?
I have a couple of the japanese rules sold by Axminster. The ones with a pearl chrome for readability and black / red markings. I use them with a Veritas stop all the time in the workshop, especially the 600mm rule.
Using a rule with the stop hooked on the edge of the board and the tip against the back edge of the track, it only takes a few iterations end to end to walk the track into parallel. You are using the same measuring device at both ends so you should get good parallelism.
You'll see how quickly the track zeros in on the correct distance. Use track clamps once you are parallel if it's a long and important cut.
Line up and make your first cut, then measure to establish the offset from the back of the track to the cutting edge. That's the offset for everything to follow using that saw and blade. You have to take a measurement and set zero with parallel guides anyway in the same way.
A ruler / stop can be swapped between tracks. All you need is to measure the offset from back of track to cutting edge. You can also use it for taking and transferring many other measurements so it will get far more use than a set of parallel guides.
