The Washington Post's In the Loop has this article on IG Reports and the FOIA. Basically they are discussing the need for Inspector General Offices to do protactive releases after investigations have been closed rather than waiting for a FOIA release and then going through the cumbersome FOIA process.
There is nothing barring agencies from making proactive disclosures rather than wait for FOIA requests. In fact, its one of the best practices touted when discussing FOIA Operations. Here is how it can work: The IG's Office closes an investigation -- its FOIA staff than process the report for privacy issues under the appropriate FOIA exemptions. The report is then posted on the electronic reading room of the agency. This cuts out the need for requesters to have to search for, request and wait for the reports.
Further, Congress can legislate these types of proactive disclosures either in the FOIA itself or when appropriating funds for IG Offices. Of course, I realize that budgets are slim but putting this type of transparency out for public consumption may save money in the long run but stopping the poor behavior in the first place (if it is known that it will be publicized).