We tried this. I used Cold Mountain rice koji to make shio koji by adding salt and water to dried koji rice and letting it ferment for 2 weeks. I made a couple loaves of
koji bread with it and had the rest sitting in the fridge. I blended it up with a stick blender and used it to marinate a NY Strip steak from the depths of the freezer for a couple days. Grilled it up and...it was fantastic. It's not a great pic but it had a great crust and we loved the savory/umami flavor from the koji.
Koji steak