I don't think there's a crane stock that exists that will hold a mini battery. The best solution would be a battery bag like this one:
http://www.airsoftparts.ca/store2/in...roducts_id=421
It will attach to your stock and you can fit the mini in there. Alternatively there are battery slings that keep the battery on the sling so it's completely off your gun. They're a little harder to find and require a bit more wire though.