Mac,
I'm thinking the only way your gonna get D* where you want is if you do the install yourself and don't involve D*.
You CAN try it yourself, but as everyone has mentioned, your tree issue is severe.
A D* installer will never be able to get a signal solid enough to pass thier tests to allow it to pass .
If you do try and set it up yourself I would expect to kn ow ahead of time that you will be having a lot of issues as the leaves fill in ...
So if this is the only position you have, your out of luck.
I would look and see what its like from the roof top as well, as much as I hate having them on the roof, if the roof puts you above the trees we don't know.
I was able to do a friends that had a situation like this, but we were able to do it as the yard next to them was cleared, so they have about a 100 ft run out to the clearing, out at the edge of thier property pointing over the neighbors.