You might want to check WikipediA's
E85 article. It talks about running E85 in nonFFVs. The author suggests running whatever mixture will consistantly leave the check-engine light off. The reason it lights up is because it's given up on controlling the mixture. I think the 1/3 rule was just a rule of thumb. Probably depends on the car. You might be able to run consistantly with about E50 without issue, although I haven't tried it.
Closest ethonal station is over 200 miles from me.