I've got a few small scrapes, almost perforations on the underside of the bottom of my wheel that have been there since the beginning. Unfortunately I didn't notice them until about a month after I bought it.
I don't see them, so I don't really worry about it too much. The only thing that bugs me is that one day those small scrapes will turn into large tears. I guess I'll worry about it then.
If yours are visible, then I agree with the others, that there isn't a great way to fix it short of replacing the whole wheel.