Carbon offsets are a sham, but you could just require them to directly pay for the actual energy infrastructure required. If you need 1GW of electricity, develop 1GW of solar.
I guess at a certain point you're getting at a more fundamental question about the value of AI (plus technology and everything else) - what level of environmental tradeoff is acceptable? One thing I slightly lament about the discourse is that tradeoff is widely discussed in the case of AI, but not in the context of stuff we do. I suspect most people aren't aware that the water use associated with eating a burger dwarves a year of ChatGPT, that a long-haul flight wipes out the emissions savings of a couple years' veganism, or that renewables have their own impacts, like the demolition of Chile for copper.