# DFV profile:
constraints => {
    customer_name => My::Customer->from_cgi
}

##</code><code>##

# object implementation
package My::Customer;

sub from_cgi {
    my $pkg = shift;
    return {
        params => [ qw/ customer_name email age / ],
        constraint => sub {
            my ($name, $email, $age) = @_;
            # untaint, trim, whatever
            return $pkg->find_or_create( ... );
        }
    };
}