I saw this a while back on Make's site that relied on the porosity of MDF as the hold down:
https://makezine.com/projects/make-4...d-down-system/ this works with an ordinary shop vac (or shop vac motor as in the build pictures. ) This clearly holds the part against some fairly significant forces from the CNC.
I don't know if this would scale down to the small size you need, though. Depends on the lateral forces that might end up being applied to the part as it's sanded and polished. 1.5" isn't a lot of area.
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