use Data::Dumper;

my @words = qw/ this Should produce Three null Values /;
my @nulls = qw/ some stuff here /;

unshift @nulls, (undef) x grep /^[A-Z]/, @words;

print Dumper \@nulls;

__ouytput__

$VAR1 = [
          undef,
          undef,
          undef,
          'some',
          'stuff',
          'here'
        ];