The "commercial" argument is a weak one and couldn't hold up to anything. You hauling anything YOU own, delivering yourself and getting paid for it is not commercial. Being paid for what is being hauled is different than being paid TO haul. In this case, that scap is your commodity. Tell em it sprouted from years of decomposing machinery, and you strictly harvested the crop and delivered to a buyer of said crop. 

Not that it's right, but plenty of people "here" hauling grain for others to the elevator on "farm" plates with CDL exemption. Hard to prove it wasn't my grain the whole trip there, just decided when I got to the elevator that I owed so-and-so for something and this load of grain was worth about the same, so I just had them put it in his name after I unloaded it. I don't know how many times someone actually had to use that or a similar story, I've been pulled over or "checked" 4 or 5 times, and not once have they ever asked to see a ticket from the elevator.