A round about way for the cash discount if you use BP or Shell at all is that they sell their gift cards at grocery stores and Walgreens. If you go the route of the Hilton Card, you get 6 points per dollar at those stores for the card purchase and then use the cards to get the cash discount. I do it all the time for BP. I used to deliver Motorhomes from Indiana to dealers and I racked up alot of points and miles buying fuel several times a day. Just be sure to tell the card company that you will be travelling or they will block your card at around the 4th station on your journey!
If the BA 100,000 deal is still alive you could get enough miles for partners there for just opening the account for several flights. Remember that the fuel is deductable unless you are using mileage and miles are tax free.
Of course I rarely flew back from a delivery, I had the dreaded Greyhound pass $499 for 60 days, you can't beat the price per mile there!

JudyJFLA