Nick, I just was "thinking out loud" again as a comment to Dennis. I have all the equipment I need -- right now.
But as long as we are talking -- a long time ago, I suggested a ball head with a long neck. A 6-12 inch neck. That single ball head would take the place of a leveler and a nadir adapter. I use a ball head right now as a nadir adapter when I use a tripod but the neck is not quite long enough to ultimately eliminate all of the tripod. I usually have to patch a little piece of one leg -- depending on how the shadows fall.
The way I use it is just flop it over so my NN3 sticks straight out at 90 degrees then adjust the upper arm to point the camera at the nadir point. Real easy and fast. And fast is good outside when shadows are moving.