If you're even close to observing the solution life suggestions Cinestill makes for Df96, and do a halfway diligent job draining the tank after your prewash, you shouldn't find dilution a major problem before the Df96 is exhausted.
Remember, fixer exhaustion, as well as developer exhaustion, extends the processing time with reuse. Do you really want to take a chance on your negatives being under-fixed because you're trying to get one or two more rolls out of your Df96?