Multiple invoices per PDF

Since recently the dutch tax authorities allow multiple suppliers to combine their invoices in in one document.
(see article at
How would you approach this in UBL? I could create one UBL document per invoice on the aggregate document, but then it's not possible to give them the same filename as the PDF.

The question/requirement was recently raised on the UBL comment list, and the TC has opened a ticket to track the status:

I think the important question, which the TC is trying to understand is: Is this a single document that includes a collection of invoices issued by a number of suppliers, or is it a single document issued on behalf of all suppliers and which replaces the need for the suppliers to issue separate invoices? Focus Areas: BPEL | DITA | ebXML | IDtrust | OpenDocument | SAML | UBL | UDDI
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