Lol, there is a thread about putting them in blenders and chopping them up to like 1/4" pieces and putting them in a tank by themselvs with a bottom full of rubble.
But, When I fraged mine I just cut then in 1/4's and made sure that part of the mouth was on each piece. But, if you can get them to move, they will usually leave behind a part of them and it will grow. I have a lot of mushrooms that I only had one of and I now have a min of 5 of each one.