This somewhat begs the question of why you are switching from a working service (DirectTV).
It would seem you other options would be to do a Dish install in September hopefully before your leaves fall where you are located and pay the couple extra months for a lower level service and then upgrade the service in December assuming it worked.
Alternatively you could just extend your Direct Service on a month to month basis until next spring when the trees have leaves again.
It sounds like the only way you are going to get an early site survey is to hire a local guy to do it for you. Dish is not going to do it unless it is along with an install order which in all honesty is a pretty reasonable request for a business to make. It would be difficult to get someone to come out and give you a landscape plan for your property without some sort of contract to pay them for it when they give you the plan.