You could steam the plywood & make a circle.
But R2 describes the frame as a polygon. It is stretching the definition of a circle to call it a polygon.
R22 requires 8" of bumper between each outside corner of a polygon. Even if you buy into a circle being a polygon, there is not 8' between outside corners.
R29A Requires the bumpers be supported by the frame 1" from each end the bumper. How can you do this if the bumpers have no end?
Not being a inspector or on the rules committee, my opinion is not the one you have to use.
Anybody notice that R22 exempts the bumpers from bag & Tag?