Search on "laguna exhaust", laguna seca exhaust, etc (which are all shorthand for the exhaust setups used at Laguna Seca Raceway where the sound is also limited) and you'll find a plethora of ideas...
Google image search=laguna+exhaust
Something like this can be quickly put together with materials from Home Depot.
Will it help enough to pass 96db? YMMV.
In my experience at Laguna Seca, you might have a chance at making 96db by focusing the sound to the drivers side (and maybe add a bolt on fart can silencer) but the only way to make 92db is to use a stock Boxster muffler.
