Onclick individual options in Zend_Form_Radio and Zend_Form_MultiCheckbox

Is there a way of giving different onclick functions for individual
options in a set of radio buttons or checkboxes? I have a javascript
function that shows a comboBox or hides it depending on which radio
button you select. This is different that giving the same function for
the whole radio button or checkbox list element, I can't see how to do
this from the library code.

Thanks for the help!