I accomplished this with a 'toggle' field. Basically you have a script associated with your desired textarea of the following:
if (TextAreaToggle.rawValue == '1') {
TextAreaField.presence = 'visible';
}else{
TextAreaField.presence = 'invisible';
}
You set the default of TextAreaToggle to '0' and then using a SetValue in the Workflow you toggle the field on at the appropriate step.
----------------
Billy Blackerby
http://tci-usa.com