Time & Material Billing Backup

Hello - most of the work we do is cost plus so we need supporting documentation to send with our invoice to our customer to be reimbursed. Our jobs consist of reimbursable items like employee travel that is loaded into the system via cash purchases, billable hours at a rate * quantity, and vendor invoices processed via AP. This leads to quite a few line items that are translated to the monthly billing. When creating a proforma, I thought the system would generate a compilation of files attached to all transactions that are reimbursable on the proforma. It doesn’t seem to do this for the printed version of the proforma or for the substantiated billing that for the proforma. Am I just missing a setting or something to be able to accomplish this? Not sure how the system could generate T&M billings but not have the backup for the T&M billing. Our VAR has of course offered a customization at a hefty price but I expect the system should be able to do this. If anyone else has went through this, I would greatly appreciate your insight!