Emailing Invoices

Hi,

I have a couple of Head Office accounts in my customer list with about 30 stores falling under the main account. We invoice the Head Office account and change the "Ship To" address to specify which store we are supplying the goods to. As far as I know we can send the invoice only to the Head Office because that's the billing account. Is there any way we can send a copy to the store receiving the goods as well? I know it can be done manually. I'm just wondering if there is an option to set up emailing the invoices to the billing address email as well as the shipping address email automatically.

Thanks