Hidden Fields in a Roo form

I need to add some hidden fields to my roo generated forms.

The attributes in input.tagx do not include hidden or readonly.

disabled isn't right since if disabled the value is not included in the post.
render = false isn't right since it doesn't put the field in the DOM

I want a hidden field as in a plain html form. I need to populate it with javascript after user input in other fields.

Spring's form tag library:
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>

in the form:
<form:hidden path="[path_name]" />

Check out "16.2.4.13 The hidden tag"http://static.springsource.org/sprin...html/view.html