Help with extending HTML_QuickForm_select

I'm working on implementing an HTML_QuickForm element for an "advanced multiple select". Basically, instead of having to ctrl+click items in a multselect it displays two multselect boxes side by side and allows you to move items between the two boxes (example at http://jalessio.com/pear/advmultselect.php). I'm using javascript to handle moving the data between the multselect boxes. Presently, the only way to get the selected items into the $_REQUEST array upon form post is to add a javascript function call to the <form> tag so it looks something like this: <form action="test.php" method="post" onsubmit="javascript:myJsFunction(blah);"> The javascript is not a problem, but this requires that I add the "onsubmit" attribute to the <FORM> tag and I'm struggling with how to properly do this within the structure of HTML_QuickForm. As far as I can tell the only chance that a class that extends HTML_QuickForm has to modify the attributes of the the <FORM> tag is via the $caller variable in the onQuickFormEvent($event, $arg, &$caller) method in my inherited class. The only way I have gotten this to work so far is by catching when onQuickFormEvent() is called with an 'addElement' event and doing something like this: $caller->updateAttributes(array( 'onsubmit' => "javascript: myJsFunction(blah)")); Is this a *correct* way to do this? Can I reliably count on being able to set this during the 'addElement' event? Any thoughts on a better way to have a subclass of HTML_QuickForm modify the attributes of the <FORM> tag that the element is going to be a member of? You can view an example of how this is currently working at http://jalessio.com/pear/advmultselect.php and please let me know if you have any problems with this in your browser of choice. Thanks for any ideas. - Jamie