You can use Blizzard's Caterpillar script in Tons of Add-ons.
# Features:
#
# - your party members follow you on the map
# - less code than other caterpillar scripts
# - use $game_player.update_buffer('reset') if you need all party members to
# gather around the player
#:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=
So you can simply have the Caterpillar deactivated by default, activate it when an event comes, and then use $game_player.update_buffer('reset') to have them gather around the hero similar to what's in the video. I haven't done this myself, but this sure sounds like something you're doing for. :X
Also, I'm not quite sure how to work the other party members going back inside the leading party member as well with this method...