I just use an old Aquadine plastic cup...cover the bottom w/ rubble or crushed coral, put the loose shroom in there, cover the bowl with some netting and use a rubberband to hold the netting on the bowl. In a week or so they'll attach to one of the pieces of rubble and you can then place it wherever you want.
I had bad luck trying to directly net the coral to a rock...the coral absolutely refused to attach (probably irritated by the netting). The bowl provides extremely low flow and good enough light so that the mushroom will attach.