Just stumbled across the 2013 Audi Exhaust treatment and would like to share :
picture source: mulsannescorner.com
picture source :Endurance-info.com
this brought me to the idea if it where not possible to create something similar -without direct connection of course to the exhaust pipe to direct air to the floor edge ..
eg a S-shaped strake (in z-x plane) ..using coanda physics to keep (exhaust) flow attached and guided to the floor edge