Consider the following picture of epiphenomenal consciousness:
We may think of mental states as having both physical and experiential components: their physical effects are due entirely to the physical aspects of our thoughts. The non-physical (experiential) component, on the other hand, constitutes what it feels like to be in that state. There's then an obvious sense in which our mental states have causal effects, insofar as their physical aspects do. That doesn't require that the causal 'oomph' come from the experiential aspect -- indeed, how could it? Experiential feels aren't the kinds of things that push atoms around. You need other particles to accomplish that!
On this view, we may (speaking loosely) say that I pulled my hand away from the hot stove "because it hurt", and this can be perfectly informative, without implying that the hurty feel itself provided the causal force that moved my hand. It's a reasonably robust explanation because across a wide range of nearby possible worlds, I flinch away from things that cause me certain kinds of pain. This is so even though the underlying physical state is what's really doing the causal work, such that if you tweaked the psycho-physical bridging laws to turn this into a zombie world, my behaviour (following my brain states) would remain unchanged. (Of course, with the robust correlation gone, the explanation "because it hurt" would no longer be available in the zombie world. My point is just that this distant possibility of correlative breakdown doesn't undermine the use of correlative explanations in the actual world.)
I think that similar "correlative" explanations are available to metaethical epiphenomenalists. Even non-naturalists who deny causal powers to abstract moral properties can nonetheless follow the likes of Sturgeon and Railton in using ethical categories in robust-process explanations. It's (in part) because Hitler was evil that his rise to power led to such atrocities. It's (in part) because American slavery was so strikingly immoral that the abolition movement gained widespread support. This isn't to say that the property of "evilness" exerted physical pressure on the world. Again, the underlying natural properties (lack of compassion, etc.) provided the causal "oomph". It's just that the moral properties correlate with important patterns of natural properties -- patterns whose various possible instantiations may reliably lead to human suffering, and to righteous indignation and outrage on the part of fitting moral agents who are attuned to those patterns.
This is all to suggest that familiar objections to (phenomenal and metaethical) epiphenomenalism seem overblown. Sure, it'd be crazy to deny (e.g.) the commonsense idea that I pulled away from the stove "because it hurt". But we've seen that epiphenomenalists need not deny this. The question then becomes: Is it so clear that commonsense commits us to the stronger claim that the hurtiness is what must provide the causal 'oomph' in such a case? I think that this is not at all clear, and that the epiphenomenalist's rival account seems perfectly sensible on reflection. But perhaps my intuitions are corrupted by theory, so I invite others to chime in with their thoughts...