I actually did get to do that for the Ohio Brew Week Judging. I got to sit with a BJCP judge (Mike Yingling), and had him help give me pointers on what to look for and how to score. I ended coming up with scoresheets that had flavors and scores consistant with him and the rest of the group. So, that was definitely helpful, and then they let me help judge the category best of show. I've begun scoring and tasting scoresheets for my own brews for extra practice. Anyway, I'm going to keep at it, and see about about getting certified once I feel I'm ready for the exam. By the way, is there a website that lists all the BJCP competitions nearby that you can judging practice.
P.S. I'll keep an eye out for you selling books at competitions, and be sure to introduce myself if I find you.