hard to tell but competing with tree roots sounds like a bad idea, and if lawn grass wont grow there either it sounds less than ideal. regular Maiden grass will grow at least somewhat in less than ideal conditions but will not get as tall or "flower". it probably will grow and live in that light but may not be very impressive

you could try Ribbon Grass which is variegated buts grows like a weed, extremely easy to divide and spread. might be anough sun for it to do okay, doesnt seem very picky about soil

Japenese Forest grass, Hakone grass, does well in just morning light but might need better soil and watered alot

You could also grow other grasses that are less sun-needy, like the Woodrushes (Luzula) and Northern Sea Oats (Chasmanthium). I have a lovely Snowy Woodrush growing in the shade and root system of a huge Black Locust, and it seems to be thriving. Sea Oats and Sweet Vernal Grass (Anthoxanthum) are in the same bed, and also doing fine.

thank you for the replies...i do think it is an impossible situation...but a large variegated grass would sure look pretty in my mind there...alas :-)