Probably lots of ways to skin that cat. I have seen guitars that just had a hole drilled in the side without any reinforcement and it worked fine. CF plastered on the inside with epoxy would help prevent cracks from originating at the hole. But I agree with Ed that it might not be the best look. I laminate a piece of side cut-off, bent to fit, to make a cross-grain patch inside. It can look good if you sandwich a contrasting veneer in the middle which gets revealed as a ring at the opening, and can tie into your purfling scheme. Binding the hole looks classy too, and affords extra protection to the rim.