Here is some info from Garf.org, what one of their visitors wrote:
After loosing many cuttings to slime, protozoan infection, I decided to cut the mushroom into four pieces like a pizza pie. After cutting them and let them heal first, until they are fully healed, in my opinion, when the disk is fully form, this will lead to stronger cuttings.
Make the cut below the disk as close as possible to the base, these cuttings are much stronger than cuttings done of just the disk of the mushroom, even if these cuttings are not attacked by protozoans. After the cuttings have been removed, dip then in a small cup of the aquarium water with a few drops of iodine for about three minutes.
For more info, you can visit <a href="http://www.garf.org/algae2/mushroom.html" target="_blank">http://www.garf.org/algae2/mushroom.html</a> and read more about it for your self. There are also other articles there about propogation.