It is normal to "spring in" the braces on a classical. Use a plane or whatever to make the bottom perfectly flat and straight. Put the top in your dish or solera, and press the fan brace in. You'll notice that it'll bend quite easily. The large braces, like the harmonic bars, I will shape to the curve before gluing them in, they they aren't so happy about bending, and arent' performing the same function as the fan braces anyway.
Some people, notably the steel string makers (
) will argue with this, stating that we should avoid all tension in the top. Maybe that's true in the SS world. But this technique goes back to at least Torres, and it works. A couple of hundred years later, and his tops still hold their shape, and sound fantastic.
As an aside, if you are serious about classical, get Romanillos' book on Torres. It's not just about the guitars, but goes into great detail about many points of construction and sound, including springing in the braces.
Note that the fan brace won't hold the 30' or whatever radius you are using. It'll flatten out a bit. But, remember that first, you will be gluing a bridge onto the top preshaped to that radius, and second, you'll have 100lbs or so of string tension. The combination will yield the proper dome.