Cervical dislocation(breaking the neck) is the only other humane way.
Honestly, you probably don't need to feed large rats to your ball pythons. That's a bit on the big side in my opinion. Most feed smalls and mediums to their adults. I personally feed smalls(70-100g) to all of my breeding adults weekly. Maybe even biweekly if I'm trying to get a snake to gain some extra size.
But it doesn't take as long to wait for the rats to grow up if you feed smalls/mediums or even 2 smalls at a time. Rat growth is pretty fast in the first 5 weeks of their life then it starts tapering and slows down. They get to small size really fast, but waiting for that large is significantly longer due to that slowing of growth.
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