Bogus email wouldnt be bad, but IP's can be traced... not necessarily illegal, rather than one of those stories about excessive spending on the tax payers dime.. $2400 bill, company credit card denied, this was from what I heard 4 nights in a hotel.. That is $600 per day... WTF are you spending that money on???
How about a good old fashioned anonymous printed letter to the Inspector General (or whomever has financial oversight responsibility) sent from a different zip code than yours?