FWIW, I do not recall ever having rented a car that was filled to the brim. And everytime I have returned one, all they look for is that the needle is pointing to the F (many of which don't budge until a few gallons have been used).

That being said, I would simply suck it up and pay the extra 30 cents or whatever per gallon at the returning State's gas price and top it off...I never have liked being THAT person who returns one less than full. I just wish more people felt that way so I knew I was really starting with a full tank...