The thread beergears posted has some decent solutions in it. My main comment would be to decide how much effort you really want to put into a corona mill - ie - do you expect to be using it for a long time, or is it just a short-term solution? Some people use them permanently and that's fine, and then it makes sense to put some effort into improving them. I didn't expect to be sticking with mine for very long, so I hardly spent a dime upgrading it, and did a lot of dirt-cheap ghetto mods instead:
Looks like crap, but it worked WAY better than the hand-cranked, tiny-hoppered, grain-spitting monster that it was originally.