I reported this same thing earlier and gave a way of doing this. I too vote for this as I suggested it a short while earlier.

Edit: My request from this thread has the solution to get hard edges, but it will affect the entire model rather than mixing the two. It's a rather simple shader and I've had this request for nearly a month now and the thread died. I've given the technique and method to doing it and it should work on shader model 1.x.