Consider the nature of the Ball Python: They roam the grasslands of equatorial africa, searching for rodent burrows. Upon finding a burrow, they will enter it and basically eat eat eat all they can. They may remain in the burrow to digest for a period of time. Given this, I don't see why it would be an issue to feed multiple prey items.

Thinking logically though, I would suspect that it is much less stress on the snake to feed a single appropriate sized prey item per feeding. Here's a few reasons I can think of:

1. Less energy spent on the snake's part.
2. Less stress due to reason above.
3. Once the snake eats, it knows nothing else edible is coming near it. You can transfer the snake back to the cage worry-free.
4. As far as digestive issues go, if you've weaned a snake eating one prey item at a time, adding another may no go over well with their system even if the snake is large enough to accomodate it.

...But then again, I am no herptologist. Just doing some critical thinking. Anyone know of any articles on this?