Conditional Form Validation

I am wondering how to use HTML_QuickForm to add conditional validation to a field.

I have a checkbox:

Code:

$t = $this->addCheckbox('website', $websitedata)->setLabel("Display Website");        

and a text box:

Code:

        $t = $this->addText('websitelink', array('size'=>50,'value'=>$data_array['websitelink']))->setLabel("Website URL");

I added the following rule to the form:

Code:

        $this->addRule('callback2','--form error--', array($this,'website_check'));

And here is my callback function:

Code:

    function website_check($val)
    {       
        $website = $val['website'];
        $websitelink = $val['websitelink'];
        if (!empty($website) ) {
            return ___('Please enter a website link value.');
        } elseif(!empty($websitelink)) {       
            return ___('If you want to display a website on our site, you must check the box to purchase the website link.');
        } else {
            return false;
        }
    }

The function executes and returns the correct value, but I don't know how to tie the error message to the websitelink field. If I don't tie the rule to the websitelink field, then I don't get the value of the checkbox sent to the callback. If I tie the rule to the form, I'm not sure how to display the error message near the websitelink field.

Any help is appreciated.

I figured this out...
$web is my checkbox and $t is the field that must contain a value if $web is checked.

Code:

$web->addRule('length', '', array(1, 10))->and_($t->addRule('nonempty', 'Websitelink is required'));