my $tmpl = new HTML::Template
    filename => 'form.tmpl.html';
my $date = new HTML::Template
    filename => 'dateinput.tmpl.html';

$date->param(ctrl_name => 'start');
$tmpl->param(start_date => $date->output);
$date->param(ctrl_name => 'end');
$tmpl->param(end_date => $date->output);

##</code><code>##

<TMPL_INCLUDE NAME='dateinput.tmpl.html' ctrl_name=start>
...
<TMPL_INCLUDE NAME='dateinput.tmpl.html' ctrl_name=end>