Page Footer whitespace

I have an invoice report that had N number of line items with N number of lines of description per line item. The invoice displays all of the line items, and then at the bottom of the last page, it provides a signature block for the customer to sign. Here is my problem: If I put the signature block in the page footer, it's displayed at the bottom - which I want - but repeated on every page. If I put the signature block in the report footer, it's displayed on the last page - which I want - but immediately following the last line item. I need it at the bottom of the last page only. The closest I have gotten is to try and predict the number of page that I will have and then hide the page footer until (what I think will be) the last page. However, this still have the page footer whitespace to show up which isn't right.