К этим полям можно получить доступ из скрипта -
https://msdn.microsoft.com/en-us/library/gg334266.aspx, а именно:
Цитата:
When a form displays a business process flow control in the header, additional controls will be added for each attribute that is displayed in the business process flow. These controls have a unique name similar to the following example: header_process_<attribute name>.