What do you mean exactly? We could plant lots of trees and make charcoal from them and bury it. That scales with the amount of money spent. The problem is that nobody wants to invest a big chunk of gdp into burying coal.
So turning trees into charcoal scales up to a certain point, but not to the point that it "would even remotely make a difference for climate change", as OP said.
Assuming that 1 kg of your proposed charcoal offsets 1 kg of mined coal, and based on [1] stating a roughly 7:1 ratio for wet wood -> charcoal, you'd need to grow more than 54.369.000.000 (54 billion) metric tons of wood per year, more to offset the harvesting, replanting, charcoaling and other processing of that wood.
I mean don't get me wrong, this is what I thought as well but it'd be a huge operation. I think you could also get away with just straight burying the wood / plant material, as long as it's anaerobic it shouldn't start rotting.
[0] https://www.worldometers.info/coal/
[1] https://forum.driveonwood.com/t/charcoal-production-rough-ru...