You could do as I have done and place the following in your Free Nodelet:

<script language="javascript"><!--

function clear_all_radios(){
    var lb = "\x5B";
    var rb = "\x5D" 
    var elements = document.getElementsByTagName('input');
    var elnum;
    for(elnum=0;elnum<elements.length;elnum++){
        var el = eval("elements"+lb+"elnum"+rb);
        if ( el.type == 'radio') {
            el.checked = false;
        }
    }
}

//--></script>
[download]

(Which I swear I got from elsewhere on this site...)

Also in my Free Nodelet, I have a link like this:

<a href="javascript:clear_all_radios()">Clear All Radios</a>
[download]

to make use of the javascript function.

Update: I seem to be getting sucked into an endless self-referential loop while looking for the source of this js. ;-)