my %hash = expand_keys(
    ['key1', 'key2', 'key3'] =>
      'Value for key1, key2, and key3',
    [qw( key4 key5 key6) ] =>
      'Value for key4, key5, key6',
    'simple key' => 'Value for simple key'
);

##</code><code>##

sub expand_keys {
    my @result;
    while(@_) {
        my $key = shift;
        my $value = shift;
        if(ref $key) {
            push @result, $_, $value foreach @$key;
        } else {
            push @result, $key, $value;
        }
    }
     return @result;
}