IMHO doing something under is even more of a pain in the rear. Applying the insulation would involve removing the stock exhaust and removing the drive shaft to get access to the front of the tunnel. You would most likely also need to unbolt the transmission brace and lower the transmission in order to squeeze your hands in there to apply the material.Is it possible to put something from under the car? Like the insulating sleeve material the active exhaust valve wires have. That way no need to take the inside apart. I'm done doing that. Ha ha. All the trim pieces I have removed incurred some damage. The cheap and flimsy plastic gets permanently deformed. It's a little, but enough not to fit like factory again. That happened with the roof console and dash trim to install the GT350 gauges, where the top of the little piece to the right of the glovebox didn't fit flush again. I was able to modify both to fit like factory again, but I wasted more time on that than the entire project. Ha ha. So unless absolutely necessary, not removing any more crap. I haven't felt any undue heat inside my Bullitt, and it's been 100+ lately, so probably not that bad. I remember other cars which felt like if a torch was there. Would like to insulate it more, so if somebody knows where to buy a material like that, and that it'd remain stuck, I'd do it for sure.
It would be easier to invest in some cheap interior panel removal tools and disassemble the center console. Review a few installation videos online that require the removal and or disassembly of the center console (MGW short shift install video).
I have owned 2 S550 5.0's and it appears to me that it is the heat that the headers/down pipes put out when it is hot outside. I have never heard any feedback about the tunnel getting hot from the EcoBoost nor the V-6 cars. I routinely notice this heat in stop and go traffic where there is not any air pushing through the tunnel area. I have also noted the tunnel is putting off heat on extremely hot days driving long distances. This is with either the stock exhaust or a aftermarket cat back exhaust system. Perhaps a transmission cooler scoop and/or insulating the underside of the console would be the only cure.