A silver (roof) lining
And of course they thought about UV protection of the Mylar! (not)
I personally would be looking at implementing this in the roof lining, plenty of usable area to play with, spatial additions could be made where conventional speakers usually go.
Let me know when you have baby "ML" panels to do this, Magnapan already are on to it.
Game on April Fool
PS: Foolproof? You haven't met our fool yet!