I have another approach that might be easier to do and/or make more sense. You would pause the sequence, take one exposure that you use for AF and when the image downloads push the 'Star Icon Button' which SGP will measures the individual star's HFR. If SGP would come up with that images HFR as a whole (like it does for the AF run), You could be able to compare that HFR with the Validation Frame's HFR. Maybe even have the Validation Frame HFR displayed in the Focus Control Module.
Really great idea overall! This only works if the exposure length is the same as your autofocus exposure length. So maybe when clicking the "Star Icon" the autofocus graph only pops up with an exposure of the same length as your autofocus exposure? Otherwise you'd need to add an additional dedicated button for this somewhere.