My limited understanding is that there's some kind of exchange happening within these mycelial networks. The plants trade hexose for phosphates and nitrates, more or less.

One hack that might be worth trying is to see if we can can supply another energy source (non food grade sugars) so that the plant doesn't end up "paying" for phosphates and nitrates with nutrients that we'd rather keep for ourselves.

Maybe that's as simple as adding compost, but it could be that some tampering is warranted to ensure that the plant gets a free ride and the fungus indeed quests after the nutrients we want it to (verses just taking our bribe and ignoring the plant, which it no longer needs as an energy source).