I do several types of gas shops. Only one allows a $5 gas reimbursement. But according to the MSC, you don't have to pump the full $5. That is just the max they will reimburse you. Of course, I don't know which shop you may be doing, but rather than wish for lower reimbursement, just check with your MSC as to whether you actually must pump the full $5 or not.
By the way, we are still at $2.49 a gallon out here and prices have started climbing again. So I don't know how much longer we will see the benefit of the lower prices.