Create GOS attachment of BUS2012 in workflow

Hi all,

I've developped an workflow for approval of purchase order. When the approver has rejected the purchase order I create a document from template to describe the the reason for rejection. Now I want to attach in the workflow this document with rejection reason to the GOS of the purchase order (BUS2012). I've an container operation to assign the document to the adhoc_attach / adhoc_object, but this is only for the workflow instance. I want that if somebody else outside the workflow displays the purchase order can see the document with rejection reason by using the GOS attachmentlist. How can I assign the document with rejection reason to the GOS of BUS2012 in the workflow?

Regards Patricia