This whole scenario was tried a few years ago. Didn't do much good. Especially when you consider that Sunoco makes the majority of the diesel in the US, and sells to the major retail stations. Also, that would only hurt the retail side, which is only paid commision for fuel sold (which isn't much commission to begin with.) Last few retail guys I talked to said they make alot more on their food and drinks than they do on the 2-3 cents a gallon they get for fuel. They basically see fuel as something to lure people into their store.