Novice - How would I add a hidden form field to a LWP::UserAgent call?

Hi,
I'm trying to post data to a server that requires a hidden form field.

This is what I'm doing:
my $content = "info=somedata";
my $rec_len = length($content);
my $send_url = new URI::URL($url);
my $hdrsend = new HTTP::Headers('Content-length' => $rec_len);
$hdrsend->header('Content-type' => 'text/html');

my $reqest = new HTTP::Request('POST', $send_url, $hdrs, $content);
my $uasend = new LWP::UserAgent;

my $resp = $uasend-> request($reqest);


The response I get back is:
<h3>Exception encountered.</h3><pre>Form post has no value for key "info".
Form values are: {}

If I create an HTML doc with a form it finds the data.  Is there something
special I need to do to get a hidden form field?

Thanks,
Chris