QuickForm - Required if

Hi, I'm trying to create a form using HTML_QuickForm. The form includes few elements that may be required, but only if another element, eg. a checkbox is active. I thought about few ways to do it, like only registering these rules on submit after manually checking if the other field is active, or using a FormRule. However both ways I'll have to give up some features like client side validation and/or denoting the field as required (unless I do it manually). Is there a cleaner way to do this? Maybe extending Rule_Required in some way? Sagi