but I think he is fundamentally taking the perfect approach: rejecting both intrincisist religious dogmatism and subjectivist moral relativism, and putting forward a third path- an objective morality discoverable by science.

I see, but as I asked before what would satisfy as "an objective morality discoverable by science."? What would the world look like if objective morality existed vs if it did not? You need to know what you are looking for, or at least have a crude sketch of how objective morality would work.