i got to talk to someone who has actually worked on diesel/ethanol blends for diesel engines (this is a PhD guy, medyo matanda na) and he says it's not really gonna fly since the basic fact is that on a per kilogram basis of fuel, pure diesel simply has more heating value (more BTU/kg).

more so for biodiesel/ethanol blends coz pure biodiesel also has a lower heating value compared to diesel. that is why in some reports, specially those soya based biodiesel, pure bd gave lower mileage figures compared to pure diesel.
of course you cannot rule out computer tweaking of fuel injection/combustion, but if that tweaking will work on bd/ethanol blend, then it would also work on pure diesel. fyi lang. ;)