Since the gas points can be earned on any happy gc, you could buy the ones for BBB and buy Disney gift cards there. However, buying at BBB can also be YMMV as some cashiers and managers do not allow using a happy gc to buy gc.
It should also be mentioned for those that haven't done fuel points before, most people will not get anywhere the 20% savings the OP projected. First of all, in many areas the price of the gas at the stations participating in the fuel points program can be much higher than the surrounding stations. (IN My area, the Shell stations are AT LEAST 30 CENTS more per gallon than the surrounding stations so there would go half the savings right away.) And then you have to have a large gas tank and try to get it pretty empty before filling up or start with the hassle of buying gas tanks and stocking up on gas. And then factor in the time and cost of driving to the store selling the happy gc's, the gas station that does the fuel points, and then to the store where you are going to liquidate the happy gc's.
The point is, fuel savings are very different than getting gift cards on sale as the savings that you get on fuel points are going to vary greatly from person to person and the savings may seem higher than it really is.