I'm confused. You initially seemed to be criticizing Greene for attempting to conclude, from individuals' responses to the dilemmas, that morality is not justifiable. I pointed out that Greene was not attempting to draw this conclusion from those data. You now say that your original argument is not a strawman because Greene would "get a good laugh" out of your alternative dilemma.

I would imagine that he might get a good laugh from this situation. After all, being an anti-realist he doesn't think there are any good reasons for moral judgments; and he might therefore find any circumstance of moral dumbfounding amusing. But I don't see how that's especially relevant to the argument.