Gosh, in days gone by when combines were less efficient, I made a lot of chaff pile sets. It's hard to find a chaff pile now, but as you said, you could make one. And I suppose that big dirthole would work too, but remember if you make way to much disturbance, some coyotes will shy off.
Honestly, in those situations I use a lot of flat sets. I use a chunk of wood for the attractor a lot of times. In soybean fields which are virtually bare, I use cow bones for attractors. In corn stubble it's going be hard to get an attractor big enough to view over the stubble, yet small enough to keep the coyotes at ease. Honestly, I try to read the wind and depend on my lure at that point.
Endeavor to persevere.