I have a client with a large gingko stump in her yard that cannot be removed due to its size and location and was wondering if it is possible to inoculate it with some edible mushroom spawn in order to obtain a yield from it and slowly shrink it in size.
What have you got to work with? I don't think there is anything specific to the gingko tree that you have to choose a particular species of mushroom to break it down. As long as you can drill into it and pack it with some plug spawn (shiitake, reishi, turkey tail, etc.), the spawn should be able to infect the whole stump and break it down.
There are some stump inoculation fungi that tend to specialize. Out here, it might be sulphur tuft or conifer tuft, back there it might be maitake, but I'm not sure. I would check with locals.