Coming from an ISP background as I do, you might be able to get around this with little coding.

We use Cricket graphing (like MRTG) to check dialup line usage for all of our gear. This tells us numerically how busy we are. We have a full report for all of our cities statically written to a website and re-gen'd daily.

We also have all the RADIUS accounting data in a sql db and scripts in front of it to check based on username, ip and start/stop date. It's not fast, but it does give us the info we want. The db stores username, ip, start time, stop time and all the other goop with radius. the search page lets you search on username, ip, start and stop times only.

This may not solve your programming problem, but it may give the higher ups enough information to get what they need without you having to break your back and reinvent the wheel 18 times