You can't. Majority of the miners are not included in the set of miners that were supposedly included. Miners will use renewable energy if it makes sense; namely lower costs or being located in a suitable geographical location. Having less than 20% of the miners openly state that they're only using renewable energy is hardly helping, media will still perceive it as a frivolous use of electricity that could otherwise be used for other more productive purposes.
As with Elon, its not about a matter of fact. Elon knows this, it was likely pressure from his shareholders that forced the Tesla announcement of dropping BTC purchases. Elon I believe has been on record stating he believes Bitcoin incentivizes green energy, although don't quote me on that.
The thing is, we don't need to prove that all miners are on green energy. We just need to show that there's a concentrated effort for them to mitigate. We might know that lower the costs, the more profit margin for the miners, so of course they aren't going to use fossil fuels for no reason, but we aren't the people that need convincing. Its the general public, and if we can refute their claims, via providing a small percentage of miners, that have openly declared what they use as evidence to back it up, I believe that will only be beneficial.
The Tesla movement was clearly a PR move, rather than Elon suddenly developing a conscious, and changing his mind with Bitcoin. I also believe he's been talking a lot about Dogecoin...so there's that too.