WordPress category permalinks

By default, WordPress category permalinks are displayed like that:

http://www.domain.com/blog/category/dogandcat

How can I shorten the /blog/ portion in the middle to /b/?

The reason behind it is: this is not a blog website, and it looks strange to have /blog/ in the URL. With that said, once I change it to /b/, it becomes un-notice-able, and at the same time, I don't change the default WPMU's permalink structure (to avoid other troubles), since the /b/ portion in the default URL is still there - just shorten /blog/ to /b/.

Please see screenshot for more details.

Thank you for reading my question