I have a bunch of them left over from my "Watchtower Bookshelf (BS)" days.
I think I might put them into a good-sized water-tight container and innoculate them with gardening fungi I have access too (non-magic variety) along with some dilute sugar solution (fungi LOVE sugar if it is dilute), let the mycellium spread through the cellulose matrix and then put them out with my yard-waste, which goes to a local compost factory (I intentionally avoided calling it a "compost plant" because that might have been confusing).
At that point, they will look HIDEOUS, but they are just friendly garden 'shrooms doing what they do best.