use warnings;
use strict;
use List::Util qw/first/;

@ARGV = qw/create --folder empty --size 50
	--additional hey how ---are --you 555/;

my $i = first { $ARGV[$_] eq '--additional' } 0..$#ARGV;
my (undef,@add) = defined $i ? splice @ARGV, $i, $#ARGV-$i+1 : ();

use Data::Dump;
dd \@ARGV, \@add;

__END__

(
  ["create", "--folder", "empty", "--size", 50],
  ["hey", "how", "---are", "--you", 555],
)