I have to agree that a whole mushroom seems most likely leed to contams.I just don't see how to clean it .Maybe a H2o2 bath would do it . I do understand the idea that the mycelium would excel and out grow the competitors . Due to the mycelium already being up and growing and the contams would have to germinate. I would be willing to try it .I have used water in a spawn jar and shaken hard, allowing the grain to bust the mycelium.Then used a syringe for innoculation in to compost .

Probably the best way would be to tear open a couple stems & use the tissue from the inside that isn't exposed to outside contaminants.