How to add a class to a dependent field's label (validate plugin)

How to add a class to a dependent field's label (validate plugin)

I've got some fields that need to validate only if a previous field returns true. I need to add a class ('required') to the dependent field's label only when that happens, so I can style it (append a red asterisk).
  1. rules: { 
  2. foo: "required",
  3. fooOther: {
  4.  required: function(element) {
  5. return $("#foo").val() == "true";
  6. }
  7. },
css:
  1. $('label.required').append('&nbsp;<span style="color:red;"><strong>*</strong></span>');
How to do?

Thanks,

--cz