Since your original post I did an experiment to propogate some blue shrooms
I have. I used to simply let them multiply where they will but in order to have some experience to share I tried the following.
I used a tweezers and firmly (really firmly, these are a little slippery) ripped a large mushroom from a rock. The gut was visible underneath (white stringy stuff). I attached it to a rock with a rubber band holding it in two places. It attached lightly in, a couple days, enough to remove the rubber band and it held (so far).
I used a new razor blade on another one, slicing as close to the rock as I could. I tried to hold this one with a rubber band as well but it wriggled free and floated off. I then used bridal veil to hold it to a rock (using a rubber band to hold the bridal veil) until it attaches.
The razor blade worked better to seperate the mushroom from the rock (with less damage IMO
A rubber band works to hold the mushroom in place but they will wriggle free and float away if they don't attach quickly. I recomemnd bridal veil.
No glue was used in either since I haven't had luck in the past holding soft organisms with glue (they hold for a day and then seperate from the glue).