Perhaps it might be better to just give up a little aero for the sake of safety?
Otherwise, look up Mcrew's Q45 belly pan build thread. I believed he used a mesh screen around his exahaust to still allow heat to dissipate through the mesh, but the screen also acts as an something for air to flow over. Essentially best of both worlds.
http://ecomodder.com/forum/showthrea...q45-11402.html