Oh. I misread your question.
I was thinking that you are asking if VF04 can be used for processing of one-time customer. Looks like you are asking if you can combine different one-time customer into one invoice.
I would check the Data Routine under Copy Control Item Level and look at ZUKRI "Combination Criteria in the billing document".
Just be cautious that SAP also hardcoded basic combination criteria on top of customization. From functional point of view, combine invoices would only make sense if it doesn't change the address and value of the invoice.
Hope this help. Would love to hear from you on the results.
Thanks
Leonard