Hi Christian, thank you for your reply!
I in deed played around with that parse action before but it was the MII Row link you shared that eventually resolved my problem. 
For others dealing with that topic: For finally mapping data to my output document, I used the Data Item Action Block. I found a helpful linkhttp://scn.sap.com/people/adarsh.sidnoor/blog/2010/11/01/dynamically-add-columns-rows-and-data-to-illumdocument-in-mii