I hear you Tammy, but what I do around 6 months is give the frozen marrow for only about 10 min.. take it away and put back in the freezer. Maybe 3 or4 days later again for 10 min. gradually working up the time that the system can handle all the marrow.
I just go "real slow" and have had good results. I also make sure I am always in the room to hear any cracking of bone, which is rare with raw/frozen and large enough bones.