Sending files to alternate customer email address


Im (currently!) a one man band field service technician. The majority of my paperwork involves issuing a service report / calibration certificate / documents to the customer, alongside the invoice, for the work done.

I would like to be able to send the invoice to one address, and my reports to the other address. For example, i attend site, fix the thing, generate the invoice and service report before i leave, and when i hit send the invoice goes to the billing emailaddress and the extra visit report attachments go to the duty manager/other emailaddress

I see i can set 2 email address for each customer. What i cannot see is a way to ensure freeagent sends the files i attach to the right address

Please advise