Remove the existing heatsink, install a heatpipe to a larger heatsink or the case itself? I'm sure there are ways to improve the existing solution.
But is it worth it?
Is the chips distortion at high power a result of current limitation, voltage limitation, heat dissipation limits or something else entirely? I can't get answers to that from the available PDF. I personally would say it's not worth it. If you have very high density, say in a rack, with tens of those modules, even a simple, slow moving fan might be enough.
They got you covered:
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