Since it didn't seem like anyone came up with a solution to this, I came up with my own tool for generating a Bearshare-compatible link from any Bitzi magnet link. It's an HTML page where you paste in the magnet URL from any (well, hopefully any) Bitzi page and it gives you a new magnet link that Bearshare can handle. Just keep a separate browser or tab open for my page while you search Bitzi so you can convert links as you search.

I wrote it in Javascript. It automatically strips out the tiger tree, kzhash, and XL tokens from the magnet URL (whichever exist), since those are the tokens that Bearshare doesn't understand. Without them, the links work perfectly.

Anyway, I hope people find it useful. Here's the URL:

http://www.plethorex.com/bitzi.html

Let me know if you come across any bugs, and send me any links that the script doesn't properly convert.