I found this thread over at clubroadster.net

Some guy has done serious aero work on his car. Custom under body panels, S2000 diffuser, APR splitter with proper supports etc.
Check out the whole thread:
http://www.clubroadster.net/forum/viewtopic.php?t=24408&postdays=0&postorder=asc&start=60
I'll never go as far as this. I might go for a splitter but thats it.