FWIW, I did find a way to do this using a brute force approach:
Unrelated, but interesting anyway: I’m finding that different brands of PETG vary in their degree of adhesion to the cryogrip plates. For instance, Sunlu HS-PETG grips much much stronger than Kingroon HS-PETG. I hadn’t thought there would be such a large difference, but there it is. For most things I actually prefer the lesser grip of the Kingroon HS-PETG, because the grip is good enough for most things and releases much easier, but I suppose if my back were against the wall on a particular print not sticking well enough, I’d first switch to Sunlu HS-PETG and try that long before switching to some other plate or even considering stronger measures like nano glue. Now, with the brute force method (above), I think those days are likely behind me anyway, but it’s always good to have stronger measures at the ready in one’s back pocket should the need ever arise.