I think there was discussion on this board earlier this summer about taking the Explore test locally. I vaguely remember that you can take Explore at your base school if an administrator/teacher is willing to administer it via the Duke TIP program if the child is 4th grade or above. I think your dc has to be registered with the TIP program first.
The processing speed concerns me as well. Coming from a private school, I don't think dd could get a 504/IEP even though she would probably qualify if she was in public school. There must be a work around here. I'm assuming a lots of Davidson applicants are coming from homeschool environments.