I was in the same situation a few years ago, where I mounted the dish in concrete in the bottom of a big flower pot. The dish ended up being pointed directly at a medium sized tree (maybe about 6-8 inches in diameter) and I still got a decent signal off of 101 (round dish).
The guy is most likely going to tell you that you won't be able to get D* due to a line of sight problem, but if you want to try for yourself I'd recomment picking up a cheap dish/receiver combo on Ebay and seeing if you can get a signal (or borrow someone's dish/receiver). You don't need a card or subscription to setup/aim the dish.
If you're after HD, you might have a harder time because you'll need to aim up with three satellites instead of just the one. I still have trouble with the spot beams on 119 due to leaves/branches in the way. Luckily though, not much on 119 these days.