Here is the answer on a thread at ecomodder.com Regular vs. Premium - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
As mentioned here, there is going to be no better without a change in timing, and at that marginal.
Check out that forum guys if you want to help your fuel costs. I was blown away at what I learned. Those guys are as good at fuel milage Hotrodders.com is at making hot rods. Believe it, they know MUCH more about that stuff than you can ever imagine!