Others who feed live can chime in but I thought that with live feeders you don't offer anything larger than a small rat, just feed more often, because rats from medium up can really do a number on your ball python.
I feed mine every five days until they get up to 500 grams, and then once a week. I have an adult male who will only take a small rat once every 10-14 days though he does get offered food weekly. The rest are good with a weekly schedule, though they'll refuse food sometimes when shedding, or during breeding season.