Hey did you see the other tip on the Miata site? It might be a little labor and require a fresh utility knife blade or other cutting technique(suggestions??), but you can slice the old timing belt, still in place, in half the long way. Then there's room to get the new one halfway on before you cut off the remnants of the old. The proper positioning is thus preserved. I always wanted to somehow do this, didn't think of the obvious. This is mainly for when you're not doing the pulleys too.
Now that I visualize it, maybe you can just make several cuts parallel to the teeth, halfway across the belt, where the pulleys are (done on an open section and then rotated to the pulley). This might also let you scoot the old one over.
But the tip for using the crescent wrenches is probably even slicker. I hadn't thought of grabbing the camshafts back there. I have done a similar trick, after the belt is off, with box wrenches on the bolts that hold on the cam belt pulleys - just to hold the darn things in place where it appears they belong.