How to make a hidden field at workflow step as required?

I have an use case that requires a hidden field to be required when user check out the form in a workflow step. I used a rule to make the field hidden in the original check-in form. When user check out and check in the form in the workflow, the field should be shown as required. I used dpPromote() iDoc Script at the Entry Event at the workflow step but it has no effect. Can this be done in the current release of the WCC workflow?