Since the Dispatcher will be quite busy, especially in the early part of the day, getting several trains heading out and so forth, perhaps another person should be tasked with directing folks to locations where they can be most useful. Since most volunteers will walk by the chalkboard on the restroom building porch, the "work dispatcher" should be there, rather than in the station. Alternatively, the work dispatcher could also be at the station or even at the shop. The point is to allow the Train Dispatcher to concentrate his full attention on the trains.
In connection with this, if the various crew leaders can estimate how many workers they might need in advance, the work dispatcher could keep track of how many folks are at each job to most efficiently distribute the volunteer workers.