No-one's really going to bother. I've known LDWA events where people have put in their own diversions of several miles...

But you're right, the spirit is to go with everyone else; remember that basically it's a group walk that allows runners to join in.

I'm not sure that saving a few seconds at the start is all that important anyway, unless you're extremely fast and looking to be among the leaders, and if that's the case, you ought to be at the bottleneck before the crowds arrive. If you think it's going to be significant, you can always sprint from the start. Personally, I intend to jog along and chat to people, and if I have to stand still for a few moments at a narrow point I won't worry.