JQuery :: Skip Validation For Fields With Empty Class

I am using the validate plugin with the defaultvalue plugin (empty fields given a default value and class of empty), and would like to use it together with the validator plugin. Is there a way to mark required fields with only the default value (and class empty) as invalid on submit?
E.g.: First_name field is required by validate, has a default value of "Enter your first name" and class of "empty" - how can I get the validator to mark this as invalid?