Invoicing

Hello,

Can anyone help me with invoicing please. I have customers who have multiple sites all of which need a separate invoice. For Example Customer 1, might have 20 different sites that we maintain several times a month. Each site has the same billing address but each site needs it's own invoice each month, showing which site the invoice is for. I use excel for the invoicing and have to use a 3rd party app to bring the information through to quickbooks, using "invoice message" as the site address. The quickbooks import function does not allow me to do this. 

Is there another way that anyone can think of? I don't want to have to pay for another years subscription to the 3rd party app which is due to renew in July. 

Thank you for any suggestions!