Done. I gave a quick read of the help file in Gubid's TBS. I recommend you should take a read too.
# Can I have events on the map that will effect the battle without being battlers?
#----------------------------------------------------------------------
# Yes. To do this simply create a event on the map named "battle_event"(without the quotes)
# Then set it up just like you always would, you can make checks against the number
# enemies/actors/neutral or practically anything you want, keep in mind, that
# the changes and checking/etc must be done via script.
If all comes to worse, you
can make those boxes neutral enemies or enemies that do not attack.
If you units to cause mutiny, select a few units and convert them to Neutral.
# How do I place actors, enemies and/or neutrals on the map?
#----------------------------------------------------------------------
# Create an event with a name including "actor","enemy" or "neutral"
# followed by a number.
# "actor1" will be the first actor in the party.
# "enemy1" will be the first enemy in the troop.
# "neutral1" that is neutral + one - will be actor 50 in the database.
# Each sequential number above 1 will be the next character.(50,51,52,53...)
# Note: Actors placed on the map must be placed in sequential order.
#
# If you want to do this during battle via event or other. In the event tell
# it to run a script with the following:
# $scene.set_character(type, id, x, y, animation_id)
# type should be "actor", "neutral", or "enemy"
# id is the ID of the actor/enemy, but remember the id entered for neutral is +50 to find the actor
# x,y isnt that obvious?
# animation_id, assign an id if you would like an animated entrance
#
This is also how you can create reinforcements. Have hidden events and then eventually after a Turns Variable reaches a certain number, make those events activate complete with enemy settings.