I found some 3/8" Baltic birch ply that seems ok for the fence. The clamp clears ok when it is at about 90 degrees, but it won't rotate much to hold down things at angles, like it does without the fence. I may cut some vertical grooves in the fence to allow for a bit more flexibility in positioning the clamp. I bought some Incra 1/4-20 knurled knobs to attach to the back of some flathead screws, countersunk in the face of the fence.
I really recommend making the fence- I had two nasty kickback episodes my first week before I made the fence. The first one actually knocked loose the little spring-loaded dust shroud that is INSIDE the blade guard. I didn't notice it right away and it slipped into the blade and cut it in half... Sigh... Festool is sending a new one. This saw seems more prone to kickback than my old Makita - maybe because the factory fences are movable and easily left too far apart? Probably user error... But the zero clearance fence and insert for below the blade seem to help the cuts a lot.