First, don't rely on JavaScript alone for form validation. JavaScript validation can be easily bypassed because the server can be accessed directly by bots (and WWW::Mechanize makes the task even easier).

Personally, i would instead use JavaScript as the confirmation page, because you still have to validate what they confirmed! Personally, i think that confirmation pages are only necessary for the deletion of records. But, having said all of that, here is some HTML::Template code that will display a confirmation page -- the trick is using hidden form fields.

use strict;
use warnings;

use CGI;
use HTML::Template;

my $q    = CGI->new;
my $tmpl = HTML::Template->new(
   filehandle => \*DATA,
   associate  => $q,
);

print $q->header, $q->start_html;

if ($q->param('cmd') eq 'confirm') {
   print $q->p("the user confirmed");
}
else {
   print $tmpl->output;
}

__DATA__
<tmpl_if cmd>
   You submitted:
   <ol>
      <li>foo: <tmpl_var foo></li>
      <li>bar: <tmpl_var bar></li>
   </ol>
   You like?
   <form>
   <input type="hidden" name="cmd" value="confirm" />
   <input type="submit" value="yes" />
   </form>
<tmpl_else>
   <form>
   foo: <input type="text" name="foo" /><br/>
   bar: <input type="text" name="bar" /><br/>
   <input type="hidden" name="cmd" value="ask" />
   <input type="submit" />
   </form>
</tmpl_if>
[download]

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
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(the triplet paradiddle with high-hat)