Looks like a very neat job there, the shield is a clever idea but I wonder how effective it is in minimising heat. I guess it will help reflect radiated heat but I am sure there is still alot of convective heat drawn in, since the air is still from the engine bay.
I think the vents could be the way to go with your idea and wondering if you could make up an aluminium cover plate with the slots cut in as deflector vanes. Polished and anodised it could have quite a visual effect consistent with the rest of the TT design. Maybe someone can get creative with Photoshop and do a mock-up.