I would have to interject and say that the clowns are most likely not happy about one of the parameters (sp?). Try changing there diet to a more diverse diet. They might not be getting the diet they think they need. I had this same issue and after paying attention to the conditions in the tank, I was able to get them to stop being canabilistic.
But you may just have f'ed up clowns who will never be happy for some unknown reason. If thats they case, good luck incubating. I've been less than successful in this technique. The key i believe is a subtle amount of flow over the eggs like the male would provide from fanning.
PS:
No, I have not read any book on clown fish nor do i profess to be the expert on them. What i can say is that I have learned from my mistakes (and in the last few months, these forums). What I say is what has worked for me in the past.