Thank you for your reply and it's so close to what I'm asking, just not quite. Let me explain further.

We work with an agency that pays for court appointed cases. Each case needs to be invoiced separately from any other cases and the case number and case name is required to show on the invoice.  This agency deals with 10s of thousands of cases per month and each case invoice is audited. It's crucial that the case number and case name be on the invoice. 

I've gotten around this problem by editing the downloaded invoice by adding text but it would be so much nicer if I could get the 'project' on the invoice too. Any hope of being able to do that?