If you have some spare crew people and access to the lights during the show, some thin
line gobos with red gels could start with the
shutter closed, and a crewman slowly pull out the
shutter during the
cue. Jiggle and light output might be concerns, and you'd probably need to make a custom
shutter to reach completely across the
shutter gate.
A moving light with a
line gobo hung just offstage and
downstage of the
drop might work, as the light spreads across the
drop during a slow pan, but every wrinkle will show as a shadow, and the fall-off of
intensity will be very noticeable.
If you have extra cast members, some
PVC pipe and thick red yarn/thin red rope could be used. Tie yarn to one pipe, and stuff inside the next pipe, tie second yarn to that pipe, and stuff into third pipe. Actors walk out together in front of painted map
backdrop, one stops, his yarn deploys, second stops, his yarn deploys,
etc. Pipes can be cut or held at different levels to match map locations, and could be decorated as bamboo or whatever seems appropriate.
A
laser might also be an option, but programming and control might be an interesting challenge.