Put some charcoal in a bucket. Use the bucket as a urinal for a few days. Mix in some of the powder that you get after polishing rice (nuka*). Cover and leave to stand for a week or so. And enjoy the absolute riot of fungus that results.
I'm not sure if this is going to be beneficial for the soil or not, but I'm fondly hoping that this is going to be the start of a truly beautiful mycorrhiza. I chucked several spoonfuls of it on a few areas of the ground cover to see if it makes any difference.
* I can't seem to say the word "nuka" normally. Whenever I'm about to say it, some kind of primitive spirit takes over and forces me to say it in a really deep voice, and then repeat "nuka - nuka - nuka" in the same deep voice while rolling my eyes. It's hardly surprising that I attribute special powers to nuka.