I do think a moral epistemology question enters into the debate that essentially removes the probabilistic underpinnings of the modal argument from evil. It seems very improbable that our moral knowledge would be directed at something objective without theism, and this especially seems true given the modal status of these worlds. These problems seem to neutralize themselves.

That being said, if you do not believe that God is a moral agent in the classical sense, you can get past this problem a bit easier. I myself am unconvinced of that there is more than one possible world, if God's wisdom is weighed in the picture. I do not think that God can sin, but I believe that in so far as the project of perfect being theology involves mere attribute consistency and does not entail God's real relation to other things. God's not being able to issue a lie flows from the fact He is the First Truth. Moreover, God as His own beatitude cannot issue a command that does not follow from His perfectly simple blessedness, something that involves the comprehension of the exemplar causes that end up constituting the human nature. Moreover, a religious attribute like holiness seems to be a pure perfection that can exist in God without entailing a moral obligation. In fact, I think the standard Judeo-Christian idea of holiness makes a great sense with divine simplicity. The Dutch theologian Jacob Arminius argued that God could only be "set apart" if He was metaphysically simple. 

I think this neutralizes a great many of the concerns that I would have as a Christian, since God's covenantal faithfulness is very important to the whole scheme of the Old and New Testament. I do not believe that this limits God and I think the countless examples that Leibniz and Anselm give provide strong enough warrant to believe this. That being said, do we have to become fictionalists about possibilities? I am unsure we do. We can simply say that when we think about possible worlds, we are participating in the divine ideas. I do not think that this amounts to ontologism, although I would not exactly fear such a possibility. While this might require a bit more than Aquinas's scheme of abstraction, I see no reason why adopting a theory like that of Saint Bonaventure would not solve the problem. Possible worlds do not cease to be real imitations of God's existence if God would only choose one world. Qua God's power, He could actualize any world. Qua God's wisdom, which is virtually distinct from His power, He might only choose one. Katherine Rogers, Paul Helm, and others offer workable solutions to this problem that I do not think lead to absurdity. Moreover, Roger's in particular offers a very workable reading of the Catechism that seems to work for any Catholics sympathetic to such a solution (as a non-Catholic, I found it a very good read).