Hmm...next project for me, think I'll make something similar to what hospitals use to spin blood samples, but for refilling cartos! I'll be fun and made of legos :3
Being a geek myself I was actually thinking of this today! (not in legos though....)
The only issue I see is making sure you get even "force" on all sides of the carto.
If I spin cartos in one direction in the battery sleeve, i get more
juice in one side then the other.
I would try to make it so that either the cartos move, or can be moved around manually periodically.
What about a salad spinner? lol Just give it a couple shakes, and you can do a large batch......