Well if it doesn't get sorted by the time you have the event maybe create another temporary board and create a special "Redirect" forum on the current one so if anyone clicks there they will get redirected........ make the new one so guests can post there and ask your members to post under their nicks so everyone knows who is who............. that way your members won't have to register and can still discuss the event.
Not an ideal solution but better then nothing.
Good luck
