The easiest way is to take the shroom and wrap cheese cloth around and over the rock the and shroom. It will take a week or so for it to take a footing, so the wrap will hold in place allowing the reefer to monitor the progress. Some people use bridal veil, rubber bands, mini holding containers inside the tank.
I, like many others have found that bridal veil or cheese cloth work with out fail when it come to slimy corals that you can not glue to rubble rock.
In the pics you can see a piece of cabbage coral I wrapped in cheese cloth and 9 days latter complete footing and rapid growth.