Here’s some good videos explaining biochar including making your own with a pyrolysis retort made from a barrel, you could apply the same charging techniques to wood chips and let them decompose for a month covered partially with a dark tarp before mixing them in, maybe turn them once a week but if you make biochar it’s ready as soon as it’s charged. All you need is an air pump which would allow you to make compost teas generally and that’s a great and mostly free way to get a ton of nice active cultures to start chewing up your dense clay.
https://www.reddit.com/r/composting/comments/zpgs80/woodchip_compost/