Is there some reason you can't do all your validation through your CGI? If not, maybe AJAX would be the way to go using the JSON module to interface with your Perl.
To disagree, one doesn't have to be disagreeable - Barry Goldwater
The trick is, for this part of the application, the application must work equally well whether JavaScript is enabled or not.
So, sure... “it's a cut-n-dry form validation chore.” And I'm probing here to find out (as is so-often the case) if “a great solution exists, but I haven't stumbled-upon it yet” among the many thousands of CPAN modules.” :-)