Morning Don
Ist the NEC code HANDbook is put out by the NFPA same folks whom bring us the code book. Its interpreations are accepted by most electrical inspectors, Two. Now you know a 250kmcm won;t fit under a 10/32 you:d be Required to use a LISTED and LABELED lug approved for that purpose.
Also in your area if its APPROVED by the AHJ (look up def of approved) You I suppose could do it. I just think Code says no and if you:ve ever put a ground screw under a cable clamp you:d know it tends to slip out as tightened because the head is so small. Ground screw have much larger heads.
Hope I started your day in a good mood. [Linked Image])