Subsidise the mining companies. Sometimes mining towns, usually companies.
Looking back to the effects of sudden cuts to mining subsidies in the UK this is somewhat understandable, but also seems kind of useless without corresponding investment in building up the economies of coal mining areas to make them more resilient and less dependent on coal in the long term, otherwise you're just delaying the pain.
Another thing to be annoyed at, there's no money for R&D for making coal power more efficient.
There is. In fact, it's something the fossil fuel industry has invested heavily in, performatively or otherwise. The problem is that you're adding complexity and cost to a technology whose only advantage is being cheap and simple, and that raises the question of why bother when you could just invest that money in renewable energy or nuclear or literally anything else.
Because at that point it's ultimately the same challenge. "Clean coal" isn't economically viable, so we need to bring down costs and build an economy of scale to make it economically viable.. except that's the same reason, and the same solution, as to why we're not using any of the alternatives available. The more you build something, the more infrastructure and industry is set up to support it, the cheaper it gets. In many countries, renewable energy is now economically viable and indeed competitive because those countries have been investing in it for decades now. US Republicans soyfacing over clean coal is just attempting to retrospectively justify the poor decision to keep investing in fossil fuels over alternatives.