User entry after approval

Hi all, I have a WF with two levels of authorization, if second approver approves then I need to ask for a reference document number and update a table with that. How can I ask for user input?

I found that is possible to ask for comments for rejection reason or to add notes for decision task.

http://scn.sap.com/docs/DOC-39687

http://www.****************/Tutorials/Workflow/UD/Index.htm

Is there other way?