Generating Invoices prior to Expiration Date

I would like to be able to generate invoices before accounts expire. For example, we like to send out an invoice on the 20th of the month for the following month. We need to do this since many of our customers take a month to process invoices which means that generally we will still not get paid until the middle to end of that month. But when I click on "Generate Invoices" it states that "There are no accounts that are due to be invoiced." Is there anyway to overide this setting?

To date, I have been going in a manually generating invoices for each account, but that is getting very cumbersome and also the Service Dates are not shown in comments unless it is automatically generated.

Any thoughts or suggestions??