I'm pretty certain I could design one that would do the job, but I'm not certain how large it would be.
And considering my design skills, it would probably look like something from a 70s Russian Tractor factory.
(My father has a 1975 Belarus 420 at home. It's a brute... )
Is there a spring at the bottom of the magazine, to push the balls back towards the chamber or whatever it's called?
Is there a way to push it back from the outside?
If so it should be possible to just empty a tube into it through a hatch.