I've heard of some people scheduling an appointment for SB100 as a back-up, but in most cases it's probably not necessary. Best bet is to choose a DMV office that has a proven track record dealing with SB100, handles the SB100 applicants as a group, and delivers the numbers.
Really no need to camp out, unless you want the full "let me tell you my SB100 story" experience.
Also, the numbers aren't in sequence, so a high number does not indicate the number of SB100 certs that remain.