The only problem with attendence lists, on the forums, is for standard members who would like to join in with the BMers, they can't add their name to the list, however...they can meet up when they get there, providing someone has got a BM flag or some other means of I D-ing the BM group.
Standard members can add to their profile that they are going to an event and would like to meet up / camp with the others, I'm sure an organiser or moderator can sort them out via PMs?
There's always a way round most things.