I've also had to do something similar to "forge" supporting documentation for medical claims. In order to claim FSA money, I had to provide detailed invoices. My hospital, however, was a big Kafka fan. They would only provide invoices that had a date and an amount, and those would take about 8 months to arrive. In order to get a detailed invoice, you had to call...but the catch is that detailed invoices were no longer available after 6 months. After every service, I'd have to immediately call for the detailed version, but if there were any after-the-fact adjustments due to insurance, I'd never be able to get a detailed statement.

To remedy this, I'd doctor previous invoices, and then print, scan, and fax to hide any editing artifacts. Keep in mind, this is all to get my own money that I'd contributed to the FSA. After that year, I just stopped using the FSA because it was such a pain.