There is not because the thought is that since the fireworks are up in the sky, they can be viewed from anywhere. (A thought I don't necessarily agree with).
We have watched Wishes from the little garden area on the right side of the castle (coming from Main Street) that is off the walkway between Main Street and Fantasyland. You can't park on the walkway itself, but you can park in the little seating areas/alcoves that are facing the castle. You are off to the side so won't see the fireworks centered over the castle, but you can see all the fireworks and have the advantage of parking the wheelchair right up to the fence so that no one can get in front of you.