I once, well twice, had a plane stuck on top of the tall shed. I tried rope with a tennis ball at the end. Didn't do a darn thing. So I had to use a ladder and go on top of the shed. I wouldn't say I'm afraid of heights, but I am afraid of being high up on something unstable. Like a wooden 25 foot ladder.
Crazy idea, what if you climbed the tree yourself using the method where you have a rope around the tree. Like this picture:
Not really to go all the way up, but high enough to get close enough to effectively use a slingshot. Or so you can effectively shake the tree. But climbing maybe too daredevil to be worth it.