I went ahead and tried this on my own using Four Starett SM44W Measure Stixs, which I was able to get for about $6.50 each. Here's a product link:
https://www.starrett.com/metrology/product-detail/SM44WThey only measure left-to-right, but the graduations are mirrored on both sides, so it does not matter.
I made a shallow knife mark in the aluminum at the 650mm mark on the parallel guides, removed the metric tape, cleaned with a razor and acetone, and applied the measure stix, aligning the 25-9/16" march with the knife mark. Prior to mounting, I cut the measure stix tape at 26" and 5-1/8", to make it easier to peel the backing and mount. This tape is a little narrower than the metric tape that came with the parallel guides, so orienting more towards the "stop" side of the guide, right where the chamfer flattens out, makes it easy to line up the pointer on the stop with your measurement. For the extensions, just cut the tape at the zero mark and.. I forget the other measurement (away from the shop now), and replace the stock tape the same way as before. Everything calibrated right up and the measure stix tape holds tight.
Prior to doing this, I did a test run by creating adding an imperial scale to the fence rail of my MFT, which I made easy to calibrate by adjusting it so the spot where it becomes thicker is exactly 8 inches from the splinter guard, so it's easy to calibrate using a square against the splinter guard, running under the guide rail, and resting against the raised area. Tested and worked perfectly and will eliminate measuring when using the MFT for 90 degree cuts against the fence... just use the stop! I'll just double check before each session, or after returning from cutting angles, that it is still calibrated.
When I get a chance, I'll try and post pictures of both, but It may be a couple of weeks.