i'm in the same position, i reckon i can fit it underneath but i'll need to make up a mounting frame.
when taking pictures earlier, i did look inside the grille, there is space in there, if your not on a nismo bumper, but you'll still need to build a custom cradle to mount it on even to fit in there.
i think where ever it goes is going to require some work. i need to do something like this regardless as when i mount my towing eye hook up i'll need to find an alternative number plate location.