sub routine {
    my $self = shift;
    my $list = &shift_list; # expose our @_
    # then @_ = ($other, $args)

    s/a/A/g for (@$list); # change the original
    ...
}

##</code><code>##

sub shift_list {
  # shift one element of @_ and return it as an array ref
  # PRESERVING the @_ aliasing
  # (if called like &shift_list we get the caller's actual @_)
  my $list;
  if(ref $_[0]) { 
    $list = shift;
    unless (ref $list eq 'ARRAY') {
      die "Not an array ref ($list)";
    }   
  } else { 
    # aliasing funkiness
    # pass aliased $_[0] to sub ref which returns a ref to it's @_
    $list = ( sub {\@_} )->($_[0]);
    shift; # for parent
  } 
  return $list;
}